PROKAS ON ESTABLISHMENT OF SPECIFIC REQUIREMENT OF

1

KINGDOM OF CAMBODIA NATION KING RELIGION

Ministry of Industry, Mines and Energy No. 701 July 17, 2007

PROKAS

ON ESTABLISHMENT OF SPECIFIC REQUIREMENT OF ELECTRIC POWER TECHNICAL STANDARDS

OF THE KINGDOM OF CAMBODIA

MINISTER OF INDUSTRY, MINES AND ENERGY

- Seen the Constitution of the Kingdom of Cambodia; - Seen the Royal KRET No. NS/RKT/0704/124 Dated July 15, 2004 on the appointment of

the Royal Government; - Seen the Royal KRAM No. NS/RKM/0196/05 Dated January 24, 1996 promulgating the

law on establishment of the Ministry of Industry, Mines and Energy; - Seen the Royal KRAM No. NS/RKM/0201/ 03 Dated February 02, 2001 promulgating the

Electricity Law of the Kingdom of Cambodia; - Seen the Prokas No. 470, dated July 16, 2004 on the establishment of Electric Power

Technical Standards of The Kingdom of Cambodia; - Seen the urgent need and real situation at present;

DECIDES

Article 1 To establish the Specific Requirement of Electric Power Technical Standards of the Kingdom of Cambodia, for implementation, in 2 main parts as below: 1- Specific Requirement of Electric Power Technical Standards for Thermal Generating

Facilities. 2- Specific Requirement of Electric Power Technical Standards for Transmission and

Distribution Facilities. Article 2 To issue the Specific Requirement of Electric Power Technical Standards in above 2 parts full contents of which are attached here with. Article 3 All electric suppliers and consumers shall fully follow this specific requirement of the Standards. Article 4 The electric suppliers are allowed to use their existing electric system for 2 years or any extension as decided by Electricity Authority of Cambodia from the date of signing of this Prokas, during which they are to improve their facilities to be in accordance with the electric power technical Standard. When the system is improved or changed or new installed, this standard shall be followed.

2

Article 5 Prokas or any decision in contradition to this Prokas shall be null and void. Article 6 This Prokas shall come into force from the date of signing.

Minister of Industry Mines and Energy Sign and Seal

SUY SEM

3

Specific Requirements for

Transmission and Distribution

Facilities

4

CONTENTS

CHAPTER 1

INTRODUCTION

Article 1: Definitions

Article 2: Purpose

Article 3: Area of Application

Article 4 : Applicable Standards

Article 5: Types of Power Transmission and Distribution Facilities

Article 6: Voltage

CHAPTER 2

GENERALS FOR TRANSMISSION AND DISTRIBUTION

PART 1

General Provisions

Article 7: Prevention of Electric Power Disasters

Article 8: Prevention of Accidents Caused by Electric Power Facilities

Article 9: Safety of Third Persons

Article 10: Prevention of Failures of Electric Power Facilities from Natural Disasters

Article 11: Prevention of Electric Power Outage

Article 12: Protection against Over-current

Article 13: Protection against Ground Faults

Article 14: Environmental Protection

Article 15: Life of Electric Power Facilities

Article 16: Requirements related to the Design of Electric Power Facilities

Article 17: Technical Documents of Electric Power Facilities

Article 18: Communication System

Article 19: Accuracy of Power Meters

PART 2

Grounding

Article 20: General Requirements for Grounding

Article 21: Classification of Grounding

Article 22: Grounding for Electrical Lines

Article 23: Grounding for Power Stations, Substations, Switching Stations and High-voltage and Medium-

voltage Users’ Sites

5

Article 24: Grounding for Distribution Lines and Low-Voltage Users’ Sites

PART 3

Conductor

Article 25: Conductors for Transmission and Distribution Facilities

Article 26: Connection of Conductors

Article 27: Safety Factor of Bare Conductors and Ground Wires of Overhead Electrical Lines

Article 28: Side-by-Side Use and Joint Use of Electrical Lines or Communication Lines

Article 29: Underground Lines

CHAPTER 3

HIGH-VOLTAGE TRANSMISSION FACILITIES

Article 30: Protective Devices for Electrical Equipment

Article 31: Design of Supporting Structures of Overhead High-voltage Lines

Article 32: Design of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines

Article 33: Protection against Lightning for Overhead High-voltage Lines

Article 34: Bare Conductors of Overhead High-voltage Lines

Article 35: Clearance between Bare Conductors and Supporting Structures of Overhead High-voltage Lines

Article 36: Height of Overhead High-voltage Lines

Article 37: Clearance between Overhead High-voltage Lines and Other Facilities or Trees

Article 38: Prevention of Danger and Interference due to Electrostatic Induction and Electromagnetic

Induction

Article 39: Surge Arresters

CHAPTER 4

MEDIUM AND LOW-VOLTAGE DISTRIBUTION FACILITIES

Article 40: Supporting Structures

Article 41: Overhead Medium-voltage and Low-voltage Lines

Article 42: Mechanical Strength of Insulators

Article 43: Medium-voltage/Low-voltage (MV/LV) Transformers

Article 44: Installation of Distribution Transformers for Single Wire Earth Return (SWER) Systems

Article 45: Protective Devices

Article 46: Height of Overhead Medium-voltage and Low-voltage Lines

Article 47: Clearance between Overhead Medium-voltage and Low-voltage Lines and Other Objects

Article 48: Proximity and Crossing of Overhead Medium-voltage and Low voltage Lines

6

CHAPTER 1

INTRODUCTION

7


In this Specific Requirements of Electric Power Technical Standards, unless the context otherwise requires,

the terms below shall have the following meanings assigned to them:

1. EAC

“EAC” is the acronym for the Electricity Authority of Cambodia.

2. Electrical Line

“Electrical Line” means the part of electric power facilities used to transmit or supply electricity.

“Electrical Line” connects power stations, substations, switching stations and user’s sites. The "Electrical

Line " also includes lines in associated protective devices and switchgears.

3. Electric Power Facility

“Electric Power Facility” means all facilities for generation, transmission and supply of electric power such

as power stations, substations, switching stations, electrical lines, dispatching centers etc... in this also

including equipment, buildings, dams, waterways, fuel storage yards, ash disposal areas, etc.

4. Electrical Equipment

“Electrical Equipment” means electrically-charged facilities.

5. GREPTS

“GREPTS” is the acronym for the General Requirements of Electric Power Technical Standards of the

Kingdom of Cambodia.

6. Guy

“Guy” means a wire to reinforce the foundation of a supporting structure. It is usually installed between

the ground and the upper part of the supporting structure.

7. High-voltage Line

“High-voltage Line” means an electrical line of voltage higher than 35kV.

8. IEC

“IEC” is the acronym for the International Electro technical Commission.

9. Insulated Conductor

“Insulated Conductor” means a cross-linked polyethylene (XLPE) insulated conductor for the medium-

voltage lines and a XLPE insulated conductor or a polyvinyl chloride (PVC) insulated conductor for the

low-voltage line.

10. ISO

“ISO” is the acronym for the International Organization for Standardization.

8

11. Joint Use

“Joint Use” means a condition that electrical lines and/or communication lines belonging to two or more

owners are installed on the same supporting structure.

12. Low-Voltage Line

“Low-voltage Line” means an electrical line having voltage of not more than 600V.

13. Medium-Voltage Line

“Medium-voltage Line” means an electrical line having voltage of between 600V and 35kV.

14. National Grid

“National Grid” is the high voltage backbone system of interconnected transmission lines, substations

and related facilities for the purpose of conveying bulk power.

15. Reversed phase-formation

“Reversed phase-formation”

means a formation of double-

circuit overhead-lines where three

phase order of one side circuit is

different from that of the other

circuit as given in the right

drawing.

16. RTU

“RTU” is the acronym for “Remote Terminal unit” for the SCADA system, installed at electric power

facilities for monitoring and controlling those facilities.

17. SCADA

“SCADA” is the acronym for “Supervisory, Control, and Data Acquisition” and refers to the equipment

used for monitoring and receiving data.

18. Side by Side Use

“Side by Side Use” means a condition that electrical lines and/or communication lines of one owner are

installed on the same supporting structure.

19. SREPTS

“SREPTS” is the acronym for the Specific Requirements of Electric Power Technical Standards of the

Kingdom of Cambodia.

a

b

c

c

b

a

Circuit 1 Circuit 2

9

20. Substation

“Substation” means the electric power facilities where voltage of electrical power is transformed and

including transformers, lightning arresters, circuit breakers, disconnecting switches, voltage transformers,

current transformers, bus bars, protective relay systems, RTU for SCADA system, telecommunication

facilities, etc.

21. Supporting Structure

“Supporting structure” means a structure that supports electrical lines, such as wooden poles, iron poles,

reinforced concrete poles and steel towers.

22. SWER

“SWER” is the acronym for the Single Wire Earth Return system. “SWER” is an electricity distribution

method using one conductor with the return path through the earth.

23. Switching Station

“Switching Station” means the electric power facilities used to change-over the electrical lines, which

include disconnecting switches, circuit breakers, bus-bars, protective relay system, the RTU for the

SCADA system, etc.

24. The Technical Standards

“The Technical Standards” means the Electric Power Technical Standards in the Kingdom of Cambodia.

25. User’s Site

“User’s Site” means any place at which machines, apparatus and devices for using electricity are installed.

Article 2: Purpose

This Specific Requirements of Electric Power Technical Standards for Transmission and Distribution

Facilities prescribes the basic requirements necessary to regulate the existing and the planned transmission

and distribution facilities in the Kingdom of Cambodia. The requirements in this standard document are

mainly for facility security and safety operation of the most important parts for facilities.


All transmission and distribution facilities in the Kingdom of Cambodia shall be in accordance with the

requirements prescribed in this Technical Standard. All persons including licensees, consultants, contractors and consumers who are related to the study, design,

construction and operation of transmission and distribution facilities shall follow these Specific Requirements

of electric Power Technical Transmission and Distribution Standards.

10

Article 4: Applicable Standards

Power transmission and distribution facilities planned to construct and operate in the Kingdom of Cambodia

shall be as per the provision of this Technical Standards. In case a matter is not stipulated in the Technical

Standards, IEC Standards shall be applied. If it is not covered in the IEC standards, ISO Standards shall be

applied. If it is not covered in the ISO Standards, internationally recognized standards shall be applied,

subject to the approval by MIME.

Article 5: Types of Power Transmission and Distribution Facilities

Power transmission and distribution facilities regulated in this Specific Requirements of Electric Power

Technical Standards has been divided into 2 types:

- High Voltage Facilities

- Medium and Low Voltage Facilities.

Article 6: Voltage 1. Standard Voltage

AC voltage shall be as follows below:

Table 1 Voltage Classification

Classification of Voltage Range of Nominal Voltage Nominal Voltage Highest Voltage

Low Voltage 600V or less 230/400V

Medium Voltage More than 600V 35kV or less 22kV 24kV

115kV 123kV

High Voltage

More than 35kV 230kV 245kV

If in the interest of development of the power sector in the Kingdom of Cambodia it becomes necessary to

use a nominal voltage other than that given in the table above, the Ministry of Industry, Mines and Energy

may allow the use of such nominal voltage as a standard voltage through issuing Prokas.

6.2 Variation of voltage

The AC voltage at low voltage power supply points shall be maintained to the value according to the

nominal system voltage in accordance with the following table:

Table 2 Voltage Variation

Nominal System Voltage Value to be Maintained

230V Between 207V to 253V

400V Between 360V to 440V

11

Notwithstanding the table above, variation of voltages can be extended only in the following cases:

- The licensee owns only low-voltage distribution line(s);

- The supply point where the voltage is out of the range of the table above is almost at the end of the

feeder;

- The voltage does not affect the consumer’s appliances;

- The licensee has obtained the consumer’s consent.

12

CHAPTER 2

GENERALS FOR TRANSMISSION AND DISTRIBUTION

PART 1

General Provisions


The electrical equipment shall be installed in such a manner that does not cause electric shock, fire and other

accidents.

Article 8: Prevention of Accidents Caused by Electric Power Facilities

The electric power facilities shall be installed with proper measures for operators not to touch their moving

parts, hot parts and other dangerous parts, and to prevent them from falling accidentally.


1. Safety of Third Persons at Power Stations, Substations and Switching Stations

Appropriate measures shall be taken to prevent third persons from entering compounds containing power

stations, substations and switching stations. These measures shall include:

a. External fences or walls to separate outside from inside compound. The height of external fences

or walls shall not be lower than 1,800 mm. Boundary Clearance from these fences or walls to

electrical equipment shall not be less than the values described in the following table:

Table 3 Boundary Clearance from Walls or Fences to Electrical Equipment

Boundary clearance [mm] Nominal voltage

[kV]

A : Height of a wall or a fence

[mm] B : Wall C : Fence

(22) not less than 1,800 not less than 2,100 not less than 2,600

115 not less than 1,800 not less than 2,100 not less than 2,600


b. Signs to alert third persons to danger shall be installed at the entrances/exits. Moreover, where

necessary, signs shall also be displayed on walls and fences.

c. Locking devices or other appropriate devices shall be installed at the entrances/exits.

13

2. Safety of Third Persons at Electric Supporting Structures

Appropriate measures shall be taken to prevent third persons from climbing supporting structures of

overhead electrical lines. To prevent danger to third persons related the supporting structures of electrical

lines the following measures shall be taken:

- Any metal steps on supporting structures shall be installed more than 1.8m from the ground.

- Warning signs to alert the third persons to danger shall be installed at each supporting structure.

- As for high-voltage lines, appropriate devices shall be installed at all legs of supporting structures to

prevent third persons from climbing the supporting structures. However, in case the supporting

structures are located at places where third persons seldom approach such as in the mountains or

where the supporting structures are surrounded by fences or walls with of an appropriate height, this

article shall not be applicable.

Article 10: Prevention of Failures of Electric Power Facilities from Natural Disasters

Proper measures shall be taken to prevent failures of electric power facilities from anticipated natural disasters

such as floods, lightning, earthquakes and strong winds

Article 11: Prevention of Electric Power Outage

- When any generating facilities have a serious fault, these facilities shall be disconnected from the

power system so that the effect of the fault on the system can be minimized and the system could be

operated continuously.

- When a power system fault occurs in a system connected to a generating facility, the generating

facility shall immediately be disconnected from the system, so that the generator runs continuously

with no-load while waiting for the recovery of the system from fault.

- When a power system fault affecting electrical lines occurs, the power cut areas shall be minimized as

much as possible by disconnecting the faulty section or by other appropriate methods.

Article 12: Protection against Over-current

1. General provision

Protection equipment against over-current shall be installed at the appropriate places of electrical circuits to

prevent electrical equipment from over-heating due to excessive current and not to cause fire.

2. Properties of Over-current Protection Equipment for High-Voltage Lines and Medium Voltage

Lines

a. Properties of fuses used for protection of over-current on a medium-voltage electrical circuit shall

conform to related IEC 60282 (2002-01) [High-voltage fuses].

14

b. Properties of circuit breakers used for protection against over-current on a medium-voltage

electrical circuit shall conform to related IEC 62271[High-voltage switchgear and control gear].

c. An over-current breaker shall have a device to indicate its switching status according to its

operation. However, if its switching status can be easily confirmed, it need not have such a device.

Article 13: Protection against Ground Faults

Protection equipment against ground faults or other appropriate measures shall be provided to prevent

damage of electrical equipment, electrical shock and fire.


1. Compliance with Environmental Standards To prevent environmental pollution, the electric power facilities shall be constructed in accordance with

the environmental laws and regulations of the Kingdom of Cambodia. 2. Prohibition of Installation of Electrical Machines or Equipment Containing Polychlorinated

Biphenyls (PCBs)

a. The installation of new electrical equipment using insulating oil that contains greater than 0.005

percent (50ppm) polychlorinated biphenyls (PCBs) shall be prohibited.

b. The use of existing electrical equipment using material containing PCBs, if it was installed before the

Specific Requirements of Electric Power Technical Standards came into force, and effective and

sufficient measures shall be taken in order to prevent the material containing PCBs from escaping

from the oil container, shall be permitted.

c. Once removed from the electrical equipment, the material containing PCBs greater than 0.005

percent (50ppm) PCBs shall not be reinstalled in another electrical facility and shall be safely

scrapped as noxious industrial wastes.

Article 15: Life of Electrical Power Facilities

Electrical power facilities shall be durable for long term usage with efficient and stable operation.

Article 16: Requirements related to the Design of Electrical Power Facilities

With regard to the design of electrical power facilities, selection of the materials, assembling and installation

of the equipment, suitable safety factors against foreseeable stresses, such as insulation strength, thermal

stress and mechanical stress shall be considered.

15

1. Insulation Co-ordination

Taking everything into consideration technically, economically and operationally, the insulation strength

of electrical equipment and facilities of an electric power system, including power stations, substations,

switching stations, transmission lines and distribution lines, shall be coordinated so that it may be in the

most rational conditions. In co-ordination of insulation the following important items shall be considered:

a. Standard Withstand Voltage of Insulation

In selection of electrical equipment, its insulation shall be suitable with the “Standard lightning

impulse withstand voltage” and “Standard short-duration power-frequency withstand voltage” given

in the table of standard withstand voltage of insulation below.

Table 4 Standard Withstand Voltage of Insulation

Nominal Voltage 22kV 115kV 230kV

Standard lightning impulse withstand voltage 95, 125, 145kV 550kV 950kV

Standard short-duration power-frequency withstand voltage 50kV 230kV 360,

395kV

b. Installation of Surge Arresters

“Lightning impulse” and “Switching impulse” shall be controlled by installing surge arresters to

coordinate them correctly.

c. Insulation Co-ordination of Power Stations, Substations, Switching Stations and Transmission Lines

In order to prevent the lightning impulse invasion to power stations, substations and switching

stations from transmission lines as much as possible, the arcing horn gaps of the steel tower near

the power stations, substations and switching stations shall coordinate with the standard withstand

voltage of electrical equipment in the power stations, substations and switching stations.

2. Dielectric Strength of Electrical Circuits

The dielectric strength of electrical circuits shall be examined by dielectric strength test, insulation

resistance measurement and so on, to ensure that their performance corresponds to their nominal

voltage.

Moreover, before starting operation, the dielectric strength shall be confirmed by charging nominal-

voltage to the circuit continuously for 10 minutes.

However, if the nominal voltage of the electrical circuit is low-voltage, it can be tested by insulation

resistance measurement or leakage current measurement. In case of the leakage measurement, it is

sufficient to keep 1mA or less.

16

3. Thermal Strength of Electrical Equipment

Electrical equipment to be installed in the substations, switching stations and high-voltage and medium-

voltage users’ sites shall be able to withstand the heat generated by electrical equipment in normal

operations.

4. Mechanical Strength of Electrical Equipment against Short-circuit Current

Generators, transformers, reactive power compensators, switching devices, bus bars and insulators for

supporting bus bars to be installed in the substations and high-voltage and medium-voltage users’ sites

shall be able to withstand the mechanical shock caused by short-circuit current.

5. Prevention of Damage of Pressure Tanks

Gas insulated equipment installed in the substations, switching stations and high-voltage and medium-

voltage users’ sites shall be designed as the following in order to avoid any risk of damage:

a. Materials and structure of the parts receiving pressure shall be able to withstand the maximum

operating pressure and shall also be safe.

b. Parts receiving pressure shall be corrosion-resistant.

c. Insulation gas shall not be inflammable, corrosive or hazardous.

d. Tanks shall withstand the gas pressure rising during fault continuous time at internal failure of

gas insulated equipment.

Article 17: Technical Documents of Electrical Power Facilities

To secure long term power supply, each facility shall have its drawings, installation records, technical manuals,

instruction manuals and operation records necessary for its proper maintenance works. These documents

shall be safekept well.

Article 18: Communication System

To secure the power supply, suitable communication facilities consisted of SCADA systems and voice

communication systems shall be provided.

1. SCADA System

SCADA systems are used to monitor and control electric power facilities and consist of RTUs,

telecommunication lines and a master station.

a. The RTU for the SCADA System shall be installed in electric power facilities so that the state of the

National Grid can be monitored and the power facilities can be controlled at the Dispatching

Center.

17

b. Necessary SCADA system shall be installed between the Dispatching Center and electric power

facilities.

2. Telecommunication Line

Necessary telecommunication lines for SCADA systems and voice communication systems shall be

installed as follows.

2.1 Installation Sites

a. Between the NCC and the Load Dispatching Center;

b. Between the Load Dispatching Center and the power facilities that compose the National

Grid.

c. Between the NCC and neighboring countries’ NCCs when the power system is connected

to a neighboring country. If there are any agreements on these systems with neighboring

countries, this may not be applicable.

Figure 1: Installation Sites

2.2 Kinds of Lines and Condition of Lines for Domestic Telecommunication line

- At least two different telecommunication lines shall be required for the National Grid.

- Lines for domestic telecommunication systems for the power system shall be provided in

accordance with Table 5.

(Legend) NCC : National Control Center

: Lines for domestic telecommunication : Lines for telecommunication to neighboring countries

Power Stations (230kV)

Substations (230kV)

Switching Stations (230kV)

Power Stations (115kV)

Switching Stations (115kV)

Load Dispatching Center

NCC NCC

Neighboring countries

Substations

(115kV)

Neighboring countries

National Control Center

18

Table 5: Type of Lines for Facilities Connected to the National Grid

Between National Control Center

and Load Dispatching Center

Between Load Dispatching

Center and Power Facilities

Data Voice Data Voice

Optical fiber 1 line 1 line 1 line 1 line

Optical fiber

Metal cable

Radio

Power line carrier

Type of Line

Microwave

1 line (selected

from 5 types)

1 line (selected

from 5 types)

1 line (selected

from 5 types)

1 line

(selected

from 5 types)

Condition of lines Exclusive line for Power System

3. Securing means of communication in an emergency

Communication facilities, which are essential to recover the power system when unexpected disasters occur,

shall be sufficiently reliable to be secure in an emergency.

Article 19: Accuracy of Power Meters

Power meters shall be accurate, fair and equitable. The accuracy of a meter shall be generally as follows:

Table 6: Accuracy of Electro-magnetic Mechanical Power Meters and Electric

Power Meters

Type of Customer *Class

High-voltage customers 0.5

Medium-voltage customers 1.0

Low-voltage customers 2.0

* In accordance with the IEC

19

PART 2

Grounding

Article 20: General Requirements for Grounding

Grounding or other appropriate measures shall be provided for electrical equipment to prevent electric shock,

danger to human beings, fire, and other trouble to objects.

Grounding for electrical equipment shall be installed to ensure that current can safely and securely flow to the

ground.

Article 21: Classification of Grounding

Grounding for electrical equipment of all electric power facilities can be classified in 4 classes as shown in the

following table:

Table 7: Classification of Grounding Work

Classification of grounding

work Resistance to earth Conditions for easement of resistance value

Class A 10Ω or less

Class B

10Ω or less

(When 1*I

230 is less

than 10, resistance

to earth shall be

the value of 1*I

230

or less.)

In the case where voltage to earth of a low-voltage electrical

circuit exceeds 230V due to power contact between the medium-

voltage electrical circuit and the low-voltage electrical circuit of

the transformer, when an earth leakage breaker that cuts off the

electrical circuit within 1 second is installed, 1*I600 Ω or less.

When 1*I

230 becomes less than 5Ω, it shall not be necessary to

obtain resistance less than 5Ω.

Class C 10Ω or less

In the case where grounding arises in a low-voltage electrical

circuit, when an earth leakage breaker that acts within 0.5

seconds is installed, the resistance value shall be 500Ω or less.

Class D 100Ω or less

In the case where grounding arises in a low-voltage electrical

circuit, when an earth leakage breaker that acts within 0.5

seconds is installed, the resistance value shall be 500Ω or less.

Remarks:

*1 - I is Single-line ground fault current (A)

20

Article 22: Grounding for Electrical Lines

The types of grounding, the places to be applied, installation conditions, and the resistance value to earth of

electrical lines shall be as given in the following table.

Table 8: Kinds of Groundings for Electrical Lines

Grounding Application Installation conditions Resistance to earth (Ω)

System

grounding

MV/LV

transformer

Low-voltage neutral conductor of TT

or TN grounding type

Value prescribed for Class B

grounding work

For high-voltage line (*2)

For medium-voltage

Value prescribed for Class A

grounding work

For low -voltage exceeding 300V Value prescribed for Class C

grounding work

Safety

grounding

Exposed

conductive

parts (*1)

For low-voltage not exceeding 300V Value prescribed for Class D

grounding work

Arrester

grounding

Surge

arrester For medium-voltage

Value prescribed for Class A

grounding work

Remarks:

(*1) “Exposed conductive parts” refers to parts such as steel stands, metal case or similar, of

apparatus installed in the electrical circuit.

(*2) Groundings for high-voltage substations and switching stations shall be individually designed,

depending on the short-circuit capacity.

Article 23: Grounding for Power Stations, Substations, Switching Stations and High-voltage and

Medium-voltage Users’ Sites

1. Grounding for Electrical Facilities

1.1 Safety Grounding

Electrical equipment to be installed in power stations, substations, switching stations and high-voltage

and medium-voltage users’ sites shall be equipped with the protective groundings listed below so that

there is no risk of rise of potential under abnormal conditions, no harm to human bodies and no

damage to other objects due to electric shocks and fires caused by high voltage invasion.

1.1.1 Grounding for Exposed Conductive Parts of Electrical Equipment

Exposed conductive parts of electrical equipment such as metal stands and metal case shall be

connected with the ground by grounding. Grounding for exposed conductive parts of

electrical equipment of different voltage is provided in the table below:

21

Table 9: Grounding for Exposed Conductive Parts of Electrical Equipment

Voltage of electrical equipment Kind of grounding work

High-voltage electrical equipment Class A

Medium-voltage electrical equipment Class A

Low-voltage electrical equipment (Over 300V) Class C

Low-voltage electrical equipment (300V or lower) Class D

1.1.2 Grounding for other facilities

Other facilities such as outdoor metal structures, external metal fences, protective metal fences

and metal stands for operation shall be provided also with grounding work according to the

voltage of the electrical facilities or equipment listed in table above.

1.1.3 Grounding for Conductive Parts in Electrical Equipment

At necessary points in electrical circuits, the grounding listed below shall be provided:

a. Grounding of Instrument Transformers (Current or Voltage Transformers)

Class A grounding work shall be provided at an arbitrarily chosen point in the electrical

circuit on the secondary side of a high-voltage or medium-voltage instrument

transformer.

In case where grounding work is provided for the electrical circuit on the primary side of

a high-voltage or medium-voltage instrument transformer, Class A grounding work shall

be provided.

b. Grounding for Station Service Transformers

In case where grounding is provided for the electrical circuit on the secondary side of

transformers connecting a medium-voltage electrical circuit and a low-voltage electrical

circuit, Class B grounding work shall be provided.

A “low-voltage electrical circuit” means an electrical circuit that supplies electricity to

automatic control circuits, remote control circuits, signal circuits for remote monitoring

devices, and the like.

c. Grounding for the Stabilizing Windings in Transformers

In case where the star-star winding high-voltage and medium-voltage transformers have a

stabilizing winding for reducing the zero phase impedance which is not connected with

outgoing electrical circuit, this winding shall be grounded with Class A grounding.

22

1.2 Grounding for Neutral Points in High-voltage and Medium-voltage Electrical Circuits

In case where grounding is provided for the neutral point of high-voltage and medium-voltage

electrical circuits in power stations, substations, switching stations and high-voltage and medium-

voltage users’ sites in order to secure reliable operation, to suppress abnormal voltage and to reduce

the voltage to ground for protective devices of electrical circuits, the grounding electrode shall be

installed to prevent risks of danger to people, domestic animals and other facilities due to the

potential difference generated between the pole and the nearby ground when any failure occurs.

1.3 Grounding for Electrical Equipment for SWER

In case where electrical equipment for SWER are installed in power stations and substations,

grounding for electrical equipment for SWER shall be provided to prevent risks of danger to people,

domestic animals and other facilities due to the potential difference between the electrical

equipment and the nearby ground caused by load current and when any failure occurs.

1.4 Grounding for Lightning Guards

The grounding resistance provided for lightning guards such as overhead ground wires and lightning

rods to be installed in power stations, substations, switching stations and high-voltage and medium-

voltage users’ sites shall be not greater than 10 Ω.

However, in case where overhead ground wires are used as SWER, the grounding work shall apply

as grounding on earth-return side of SWER provided above.

1.5 Grounding for Surge Arresters

The grounding resistance provided for surge arresters for high-voltage and medium-voltage


voltage users’ sites shall be less than 10 Ω as much as possible to prevent hindrance to the functions

of the surge arrester

2. Particularities of Grounding Arrangement

2.1 Properties of Grounding Conductors

Grounding conductors to be installed in electrical circuits in power stations, substations, switching

stations and high-voltage and medium-voltage users’ sites shall be constructed of corrosion-resistant

metallic wire and shall be able to carry the current safely during failures.

a. Mechanical Strength of Grounding Conductors

In order to secure necessary mechanical strength, the grounding conductors listed in Table 9 shall

be used, depending on the kind of grounding work for which the grounding conductor is used.

23

Table 10: Grounding Conductors to be used for Grounding Work

Metal wire Annealed copper

wire

Annealed copper

twisted wire

Kind of grounding conductors

Kind of grounding work

Tensile strength Diameter

Sectional Area

Grounding conductors for

neutral points of high-voltage

and medium-voltage electrical

circuits in generators and

transformers

not less than 3 kN not less than 4 mm not less than 14 mm2

Clas

s A

Others not less than 2 kN not less than 3 mm not less than 6 mm2

Clas

s B

Low-voltage side neutral

points of transformers

transforming medium-voltage

into low voltage

not less than 2 kN not less than 3 mm not less than 6 mm2

Class C not less than 1kN not less than 2 mm not less than 4 mm2

Class D not less than 1kN not less than 2 mm not less than 4 mm2

b. Thermal Strength of Grounding Conductors

Grounding conductors in which grounding current flows when any abnormality occurs, such as

those for neutral points of electrical equipment and high-voltage and medium-voltage electrical

circuits, shall have also enough thermal strength against the heat from grounding current

during the occurrence of such abnormality or failures in addition to mechanical strength.

2.2 Installation of Grounding Conductors

Grounding conductors for instrument transformers, neutral points, surge arresters and SWER to be

installed in power stations, substations, switching stations and high-voltage and medium-voltage users’

sites shall be grounded directly to the ground without being connected to stands of equipment. Bare

live parts of grounding conductors shall be installed so that there is no risk of operators easily coming

into contact with them.

2.3 Neutral Grounding Devices

Resistors and reactors to be connected to grounding conductors in power stations, substations,

switching stations and high-voltage and medium-voltage users’ sites shall be suitable and safe for the

flows of electric current when any failure occurs.

24

Bare live parts of resistors, reactors and other neutral grounding devices shall be installed so that there

is no risk of operators easily coming into contact with them.

2.4 Prohibition against Installation of Switching Devices on Grounding Conductors for Neutral

No switching device and power fuse, excluding switching devices to be installed to switch neutral

resistors and neutral reactors, shall be installed on grounding conductors for neutral in power stations,

substations, switching stations and high-voltage and medium-voltage users’ sites.

2.5 Connection between Grounding Conductors

Grounding conductors of earth-return side of SWER to be installed in power stations and substations

shall not be connected to the grounding conductors of other electrical equipment.

Article 24: Grounding for Distribution Lines and Low-Voltage Users’ Sites

1. Particularities of Grounding Arrangement

Grounding for distribution lines and low-voltage users’ sites shall be installed according to the following.

1.1 Grounding Electrodes

1.1.1 Materials and dimensions of the grounding electrodes shall be selected for corrosion resistance

and adequate mechanical strength.

1.1.2 The following are examples of grounding electrodes which may be used:

a. Metal plates

b. Metal rods or pipes

c. Metal tapes or wires

d. Underground structural networks embedded in foundations (foundation grounding)

e. Other suitable underground metalwork approved by MIME

1.2 Grounding Conductors and Protective Conductors

Protective conductors in this provision mean the conductors used for connecting electrical equipment

to the grounding system.

a. Grounding conductors and protective conductors shall be constructed of corrosion-resistant

metallic wire and shall be able to carry the current safely at failures.

b. Grounding conductors shall comply with paragraph c and, where buried in the soil, their cross-

sectional areas shall be in accordance with Table 11A.

25

Table 11A: Minimum Cross-sectional Areas of Grounding Conductors Buried in the Soil

Conditions Mechanically protected Mechanically unprotected

Protected against corrosion 2.5 mm2 Cu (Copper)

10mm2 Fe (Iron)

16mm2 Cu (Copper)

16mm2 Fe (Iron)

Not protected against corrosion25mm2 Cu

50mm2 Fe

c. The cross-sectional area of protective conductors shall be selected in accordance with Table

11B or paragraph d.

Table 11B: Minimum Cross-sectional Area of Protective Conductors

Minimum cross-sectional area of the corresponding

protective conductor (mm2)

Cross-sectional area of

lineconductor, S (mm2) If the protective conductor is the

same material as the line conductor

If the protective conductor is not the

same material as the line conductor

S≤16 S k × S

16<S≤35 16 k × 16

S>35 S/2 k × S/2

*k is selected from Table 11C.

Table 11C: Factor k, for Table 11B

Materials of protective conductors

Aluminum Copper Steel

Materials of

line conductors

Conductor insulation

PVC Rubber PVC Rubber PVC Rubber

PVC <300mm2 - - 0.58 0.48 1.56 1.32 PVC >300mm2 - - 0.52 0.43 1.39 1.18

Aluminum

EPR / XLPE - - 0.71 0.60 1.92 1.92 PVC<300mm2 1.31 0.73 - - 2.45 1.99

PVC >300mm2 1.18 0.65 - - 2.11 1.78

Copper EPR/ XLPE 1.63 0.90 - - 2.92 2.47

*Note: Factor k provided here is used only for insulated protective conductors not incorporated in

cables and not bunched with other cables. In case of other protective conductors, the factor shall

follow IEC60364-5-54.

26

d. The cross-sectional area of every protective conductor which does not form part of the cable

or which is not in a common enclosure with the line conductor shall be not less than the size

given in Table 11D.

Table 11D: Cross-sectional Area of Protective Conductors (IEC60364-5-54）

Mechanically protected Mechanically unprotected

2.5mm2 Cu

16mm2 Al

4mm2 Cu

16mm2 Al

1.3 Installation of Grounding Electrodes and Conductors

In case there is any danger of persons touching grounding conductors, electrodes and conductors for

Class A and Class B shall be installed as described below:

a. Grounding electrodes shall be installed at depths of not less than 75cm underground.

b. Grounding conductors shall be covered in the section from 75cm underground to 2.0 m above

ground by a synthetic resin pipe or another shield of equivalent or higher insulating effect and

strength.

c. If the grounding electrode is installed along iron poles or other metallic objects, insulated

conductor or cable shall be used for the full length of the grounding conductor.

d. If the grounding electrode is installed along iron poles or other metallic objects, the grounding

electrode shall be buried with a clearance of not less than 1m from those metallic objects.

In case where the grounding electrode is installed along iron poles or other metallic objects, the

clearance between the top of the electrode and the bottom of iron poles or other metallic objects

shall be not less than 30 cm.

2. Class B Grounding Resistance

Single-line ground fault current (I) of an electrical circuit in the medium-voltage side used for calculation of

resistance of Class B grounding provided in Article 21 of these SREPTS shall conform to an actual value, or

the following:

2.1 Medium-voltage Electrical Circuit of Isolated Neutral System

Class B grounding resistance for isolated neutral systems shall be determined by the following:

a. Electrical circuits using an electric conductor other than a cable

For electrical circuits using an electric conductor other than a cable, Class B grounding resistance

shall be not more than ten 10 Ω.

b. Electrical circuits using a cable for an electrical conductor

27

For electrical circuits using a cable for an electrical conductor, Class B grounding resistance

shall be determined by Table 11E and Table 11F according to the total length of medium-

voltage circuit (limited to that using a cable for an electrical conductor) connected to the same

bus.

Table 11E: In Case Class B is Decided by 230/I

L <3km 3km≤

Class B grounding resistance (Ω) 10 5

Table 11F: In Case Class B is Decided by 600/I*

L <4.5km 4.5km≤

Class B grounding resistance (Ω) 10 5

* In case of an earth leakage breaker that cuts off the electrical circuit within 1 second

Where:

L: the total length of medium-voltage circuit (limited to that using a cable for an electrical

conductor) connected to the same bus.

c. Electrical circuits using an electrical conductor other than cable and also a cable for an electrical

conductor

In this case, Class B grounding resistance shall be determined by Table 11E and Table 11F

according to the total length of medium-voltage feeders (limited to that using a cable for an

electrical conductor) connected to the same bus.

2.2 Medium-voltage Electrical Circuit of Solidly Grounded Neutral System

Single-line ground fault current (I2) of an electrical circuit in the medium-voltage side used for

calculation of grounding resistance in Class B grounding provided in Article 21 of these SREPTS

shall conform to an actual value, or the following formula.

* Any fraction less than the decimal point shall be rounded up.

Where:

I2: Single-line ground fault current (A);

I1: Single-line ground fault current of the electrical circuit in case of no solidly system grounding

which is calculated by a theoretical formula (A);

V: Nominal system voltage of the electrical circuit (kV);

62

22

12 10R3VII ×+=

28

R: Electric resistance value of the resistance used in the neutral point (including the resistance to

ground value of the neutral point) (Ω);

3. Grounding Systems for Low-voltage Lines

Grounding systems for low-voltage lines have 2 types: TT and TN. These grounding works shall comply with

IEC 60364-1.

a. The TT system has one point directly grounded and the exposed-conductive parts of the installation

are connected to ground that are electrodes electrically independent of the ground electrodes of the

power system.

b. The TN system has one point directly grounded and the exposed-conductive parts are connected to

the point by protective conductors. Two types of TN system are considered according to the

arrangement of neutral and protective conductors, as follows:

- TN–S system: in which, throughout the system, a separate protective conductor is used;

- TN-C system: in which neutral and protective functions are combined.

c. Low-voltage electrical equipment to be installed at users’ sites shall be installed according to the IEC

60364 series. If it is directly connected to a power supplier, the grounding system shall be the same

as that of the supplier’s equipment involved in the supply of low-voltage electricity.

Low-voltage electrical equipment shall not be installed in such a manner that the grounding systems

are different from those used at the same user’s site.

(LEGEND) Neutral Conductor (N) Protective Conductor (PE) Combined Protective and Neutral Conductor (PEN)

System Grounding

L1

L2

L3

N

Exposed-conductive-parts

PE

29

Figure 2: TT System

Figure 3: TN-S System

System Grounding

L1

L2

L3

N


PE

System Grounding

L1

L2

L3

PE


System Grounding

L1

L2

L3


PE

30

Figure 4: TN-C System

System Grounding

L1

L2

L3

PEN


PE

N

System Grounding

L1

L2

L3

PEN


31

PART 3

Conductor

Article 25: Conductors for Transmission and Distribution Facilities

1. Generals

The conductors for transmission and distribution facilities shall be cables, insulated conductors or bare

conductors. Bare conductors shall not be used for low-voltage lines.

Cables and insulated conductors shall have sufficient insulation capacity appropriate for the conditions of the

applied voltage.

2. Property of Conductors

2.1 The conductors shall withstand temperatures under ordinary use.

2.2 The structure of the conductors

a. Insulated Conductors

The structure shall be an electric conductor covered with insulating material.

b. Cables used in Low-voltage Line

The structure shall be such that an electric conductor is covered with insulating material that is

protected with armor.

c. Cables used in Medium-voltage Line

The structure shall be such that an electric conductor is covered with insulating material that is

protected with armor, and that has a metal electric shielding layer made of metal provided on the

cable core in a single-core cable, and on the cable cores bundled together, or on each cable core

in a multi-core cable.

2.3 The conductors, the completed product to be used in a transmission line, or in a distribution line

shall pass an appropriate AC withstand voltage test.

2.4 The tensile strength per unit area (MPa) of hard-drawn aluminum wires used for single conductors in

an overhead line shall be not less the value given in Table 12 conforming to the related IEC

standards.

32

Table 12: Tensile Strength of Hard-drawn Aluminum Wires (IEC 60889)

Nominal diameter

Over (mm) Up to and including (mm) Minimum tensile strength (MPa)

- 1.25 200

1.25 1.50 195

1.50 1.75 190

1.75 2.00 185

2.00 2.25 180

2.25 2.50 175

2.50 3.00 170

3.00 3.50 165

3.50 5.00 160

Article 26: Connection of Conductors

Conductors shall be connected as per following methods:

a. Conductors shall be connected firmly and the resistance of conductors shall not increase more than

the resistance of conductors without connection.

b. Conductors shall be connected so that the insulating capacity of cables and insulated conductors

shall not decrease less than the insulating capacity without connection.

c. With regard to connecting conductors of different kind of materials, electrochemical corrosion shall

be prevented.

Article 27: Safety Factor of Bare Conductors and Ground Wires of Overhead Electrical Lines

1. Generals

As for tensile strength of conductors and ground wires for overhead electrical lines except for cables, the

safety factor shall be 2.5 or more.

2. Loads on Conductors for Overhead Transmission Lines

2.1 Assumed Load and Safety Factor

Overhead transmission conductors and overhead ground wires (excluding cables, the same applies

hereafter in this clause) shall be installed with the tension to allow a safety factor specified in the

33

following Item 2.1.2 when they are subject to the assumed load specified in the following Item 2.1.1

below at the average temperature in the area.

2.1.1 Assumed Load

The assumed load for the calculation of tension of overhead transmission conductors and overhead

ground wires shall be the composite load of the vertical loads specified in the following item a and

the horizontal loads specified in the following item b.

a. The vertical load shall be the weight of the electrical conductor.

b. The horizontal load shall be the horizontal maximum wind pressure load of the electrical

conductor’s vertical projected area.

2.1.2 Safety Factor

A safety factor of 2.5 or more shall be applied to the tensile strength (ultimate tensile strength;

breaking strength) of overhead transmission conductors and overhead ground wires.

2.1.3 Reference Wind Velocity

Reference wind velocity to design overhead lines shall be as given in Table 13.

Table 13: Reference Wind Velocity

Yearly maximum of 10-minute average wind velocity

(50 year return period) 32 m/sec

In the following circumstances, the above reference wind velocity can be changed.

a. When sufficient observed data have been accumulated.

b. When greater reliability is especially needed.

c. When the design is needed to cooperate with the designs of neighboring countries.

34

Figure 5: Assumed Load

2.2 Every Day Stress of conductors

EDS* (Every Day Stress) of conductors shall be considered to avoid conductor’s fatigue in overhead

lines due to aeolian vibration.

* EDS is expressed as the percentage of ultimate tensile strength (UTS) under windless condition.

Article 28: Side-by-Side Use and Joint Use of Electrical Lines or Communication Lines

1. High-Voltage Lines, Medium-Voltage Lines and Low-Voltage Lines

Side-by-side use and joint use of electrical lines shall be done by the following methods.

1.1 High-voltage Lines and Medium-voltage Lines

a. When a high-voltage line and a medium-voltage line are installed at the same supporting

structure, the medium-voltage line shall be installed under the high-voltage line and on

separate crossarms.

b. The clearance between any overhead high-voltage line conductors and any overhead medium-

voltage line conductors shall under no circumstances be less than the values specified in

Article 37 of these SREPTS at any point in the span.

c. The overhead high-voltage line conductor shall be stranded wire with a tensile strength of at

least 30kN, unless they are cables.

d. The nominal voltage of the high-voltage electrical lines in side-by-side use or joint use shall

be not more than 115kV.

b. The horizontal maximum wind pressure load

Composite load

a. The weight of the electrical conductor

Support

Support

35

1.2 Medium-voltage Lines and Low-voltage Lines

1.2.1 When a medium-voltage line and a low-voltage line are installed at the same supporting

structure, the low-voltage line shall be installed under the medium-voltage line and on

separate cross arms.

1.2.2 The conductor of the low-voltage line shall be conformed with following provisions, except

in cases where cables are used:

a- In case the span of the low-voltage line is shorter than 50m, the tensile strength shall

be not less than 5kN.

b- In case the span of the low-voltage line is 50m or over, the tensile strength shall be

not less than 8kN.

1.2.3 The low-voltage line in a part installed on the same supporting structure of an overhead

medium-voltage line shall be grounded with class B grounding and its resistance shall be not

more than 10Ω.

1.2.4 The clearance between any overhead medium-voltage line conductors and any overhead low-

voltage line conductors shall under no circumstances be less than the values specified in

Article 48 of the SREPTS at any point in the span.

1.3 High-voltage Lines and Low-voltage Lines

1.3.1 No low-voltage line shall be installed at the same supporting structure where a high-voltage

line is installed.

1.3.2 Exception of Side-by-side Use of High-voltage Lines and Low-voltage Lines

Side-by-side use of high-voltage lines and low-voltage lines is permitted only if all following

measures are taken to intensify the facilities.

(1) The conductor of the low-voltage line shall be conformed with following provisions,

except in cases where cables are used:

a. In case the span of the low-voltage line is shorter than 50m, the tensile strength

shall be not less than 5kN.

b. In case the span of the low-voltage line is longer than 50m, the tensile strength

shall be not less than 8kN.

(2) The low-voltage line in a part installed on the same supporting structure of an overhead

high-voltage line shall be grounded with Class B grounding and its resistance shall be not

more than 10Ω.

36

(3) The clearance between any overhead high-voltage line conductors and any overhead low-

voltage line conductors shall under no circumstance be less than 4.5m at any point in the

span.

(4) The overhead high-voltage line conductor shall be stranded wire with a tensile strength of

at least 30kN unless they are cables.

(5) The nominal voltage of the high-voltage line shall be not more than 115kV. In case the

high-voltage line has double circuits, reversed phase-formation shall be adopted.

(6) The distance of side-by-side use of high-voltage lines and low-voltage lines shall be decided

taking the assumed induction voltage into consideration.

(7) Exception can be allowed in the following unavoidable circumstances:

a. There is no suitable space to install a low-voltage line in urban areas, because houses

stand close together and the only appropriate low-voltage line route is along a road but

a high-voltage transmission line has been already installed there.

b. Other special circumstances approved by the EAC.

2. Electrical Lines and Communication Lines

Side-by-side use and joint use of electrical lines and communication lines shall be done by the following

methods. If communication lines consist of optical fibers and they are tied to electrical lines or ground wires,

this may not be applicable.

a. When a medium-voltage or a low-voltage line and a communication line are installed on the same

supporting structure, the medium-voltage or the low-voltage line shall be installed above the

communication line and on separate cross arms.

b. No communication line shall be installed at the same supporting structure where a high-voltage line

is installed.

Article 29: Underground Lines

1. Conductors of Underground Lines

Cables shall be used for underground electrical lines.

2. Draw-in Conduit System and Culvert System

a. In case underground lines are installed with a draw-in conduit system, tubes of the draw-in conduit

system shall have sufficient strength to withstand the pressure of vehicles and other heavy objects.

b. In case the strength of the tubes cannot be verified, they shall be installed not less than 1.2 m in

depth to prevent a danger due to the pressure from vehicles and other heavy objects.

37

c. In case underground lines are installed with a draw-in culvert system as shown in Figure 6 B, culverts

shall be capable of withstanding the pressure of vehicles and other heavy objects.

Figure 6A: Example of Draw-in Conduit System

Figure 6B: Example of Draw-in Culvert System

3. Direct Burial System

3.1 In case underground lines are installed with a direct burial system, they shall be installed in

accordance with the following methods.

a. Installation of proper plates above the underground lines or other proper measures shall be

taken to protect the underground lines against mechanical shocks.

b. The installed position of underground facilities shall be not less than 1.2 m in depth at a place

where there is a danger of receiving pressure from vehicles or other objects, and not less than

0.6 m at any other place.

Steel, plastic, or polyvinyl chloride tube Concrete

Rack for cable

38

3.2 The depth of underground facilities described in 3.1.b above signifies the depth of such facility

measured from the plate to protect cables.

3.3 The following places shall be included among the ‘any other place’ of 3.1.b above.

a. The sidewalk of a road.

b. A road where no cars pass.

Figure 6C: Explanation of the Depth of the Direct Burial System

D

Brick, warning tape etc.

Lid

Sand

Trough

D

Trough

D

39

Table 14A: Depth in case of Direct Burial System

At a place where there is a danger of receiving pressure

from vehicles or other objects D = Not less than 1.2 m

Other place D = Not less than 0.6 m

4. Clearance between Multiple Underground Lines

4.1 Minimum clearance between a new underground line and other electrical lines shall be as shown in

the following table:

Table 14B: Clearance between Multiple Underground Lines

(Unit: m)

Other electrical lines New line

Low voltage Medium voltage High voltage

Low-voltage 0.15 0.3 0.3

Medium-voltage 0.3 0.3 0.3

High-voltage 0.3 0.3 0.3

4.2 In case one of two electrical lines is installed in an incombustible stout tube, the minimum

clearance shall not be required.

5. Clearance between Underground Lines and Other Facilities

a. Minimum clearance between a new underground line and other facilities shall be as shown in

the following table:

Table 14C: Clearance between Underground Lines and Other Facilities

(Unit: m)

Other facilities New line

Communication line Gas Water Sewerage

Low voltage (*0.1)

0.3 Shall not make direct contact

Medium voltage (*0.1)

0.6 1.0 0.3 0.3

High voltage 0.6 1.0 0.3 0.3

* The approval of the owner of the communication line shall be required.

40

b. In case the electrical line is installed in an incombustible stout tube and the tube does not come

into direct contact with other facilities, the minimum clearance shall not be required.

c. In case communication lines are united with electrical lines, the minimum clearance shall not be

required.

6. Connection of Underground Cables

The connection of underground cables shall be implemented with the following methods, in addition to

Article 26 of these SREPTS.

a. The connecting device shall be able to withstand the external forces that will be extended under

the expected conditions.

b. The connected cables shall be in good order for the permissive current of the original cables.

c. The connected cables shall have same waterproof performance.

7. Structure of Underground Boxes

In case underground boxes are installed, their structure shall be as follows:

a. The underground boxes shall be able to withstand the pressure of vehicles and other heavy

objects.

b. When there is some possibility that explosive gases or combustible gases are filled in the box

and the capacity of the box is 1m3 or more, a device such as a ventilator to exhaust the gases

shall be installed.

c. The lids of underground boxes shall be so installed that third persons are unable to open them

easily.

8. Grounding for Underground Facilities

Safety grounding of Class D shall be installed at the metallic part of such facilities as the tube, culvert and

joint box, and the metallic shield tape of a cable.

41

CHAPTER 3

HIGH-VOLTAGE TRANSMISSION

FACILITIES

42

Article 30: Protective Devices for Electrical Equipment

1. Measures for protecting Conductors and Electrical Equipment against Over-current

At necessary points in electrical circuits, over-current circuit breakers that protect against heating damage by

over-current and prevent outbreaks of a fire shall be installed.

2. Protection and Alarm Devices for Transformers and Reactive Power Compensators

Transformers and reactive power compensators to be installed in stations and high-voltage and medium-

voltage users’ sites shall be equipped with devices to automatically cut off the transformer and the reactive

power compensator from the electrical circuit when any abnormality that might cause significant damage and

serious trouble to the supply of electric power occurs, in addition to other appropriate protection systems, as

shown in Table 15.

Table 15: Protection Systems for Transformers and Reactive Power Compensators

Protection and alarm device

Classification Abnormality Automatic

shutdown device

Alarm

device

Over current ---

Internal fault --- Common

Significantly rise in temperature ---

Main

transformer

Transformer with cooling system

(A cooling system in which the

coolant is sealed-in to directly

cool the windings and iron core

of the transformers, and is

forcibly circulated)

When the cooling system fails or

when there is a significant rise in

the temperature of the

transformer

---

Power

capacitor Common

Over current or over voltage

or internal fault ---

Over current ---

Internal fault --- Common

Significant rise in temperature ---

Shunt

reactor

Shunt reactor with cooling

system (A cooling system in

which the coolant is sealed-in to

directly cool the winding and

iron core of the shunt reactor,

and is forcibly circulated)

When the cooling system fails or

when there is a significant rise in

the temperature of the Shunt

reactor

---

Notes- : Equips

-- : No need

43

Article 31: Design of Supporting Structures of Overhead High-voltage Lines

1. Basic Conditions

a. Supporting structures of overhead lines shall be designed, taking into account the following loads.

Table 16A: Type of Loads

Type of Load Components of Load

Weight of the supporting structure

Weight of the conductors and the ground wires and the accessories supported by the

supporting structure

Weight of the insulator strings and the fittings supported by the supporting structure Vertical loads

A vertical component of the maximum tension of the guy wires supporting the

supporting structure, if any

Wind pressure on the supporting structure under the maximum wind velocity

Wind pressure on the conductors and the ground wires supported by the supporting

structure under the maximum wind velocity

Wind pressure on the insulator strings and the fittings supported by the supporting

structure

Horizontal

transverse loads

A horizontal transverse component of the maximum tension of the conductors and

the ground wires supported by the supporting structure and the guy wires supporting

the supporting structure, if any

Wind pressure on the supporting structure under the maximum wind velocity Horizontal

longitudinal

loads

A horizontal longitudinal component of the unbalanced maximum tension of the

conductors and the ground wires supported by the supporting structure and the

maximum tension of the guy wires supporting the supporting structure, if any

b. Supporting structures and foundations of overhead high-voltage lines shall be designed, taking the

value of wide pressure based on the reference wind velocity prescribed in Article 27 of these

SREPTS into consideration.

c. Supporting structures and foundations of overhead high-voltage lines shall be designed to withstand

the maximum loads, taking appropriate safety factors into consideration.

d. In case overhead high-voltage lines are installed at places with the worst conditions, such as inside

river areas, windy areas, and so on, the supporting structures and the foundations shall be designed

to withstand such severe conditions.

44

2. Components of Supporting Structures

Components of supporting structures shall satisfy the following or shall have an equivalent strength to these

items.

2.1 Fundamental Properties of Components of Supporting Structures

Flat steel, shaped steel, steel pipes, steel plates, steel bars and bolts which compose a steel tower or an

iron pole used for overhead transmission lines shall be appropriate ones as specified in the ISO

(International Organization for Standardization) standards or other standards equivalent to these

standards.

2.2 Thickness of Steel Members etc.

Shaped steel, steel pipes and steel plates to be used for a steel tower or an iron pole for overhead

transmission lines shall have the thickness and other dimensions specified below.

2.2.1 Minimum Thickness of Shaped Steel

a. Those to be used as a main post member of an iron pole (in which a main member of a

cross arm is included. The same shall apply hereafter in this article) shall have a thickness of

4 mm.

b. Those to be used as a main post member of a steel tower shall have a thickness of 5 mm.

c. Those to be used as other structural members shall have a thickness of 3 mm.

2.2.2 Minimum Thickness of Steel Pipes

a. Those to be used as a main post member of an iron pole shall have a thickness of 2 mm.

b. Those to be used as a main post member of a steel tower shall have a thickness of 2.4 mm.

c. Those to be used as other structural members shall have a thickness of 1.6 mm.

2.2.3 Slenderness Ratio of Steel Members

The slenderness ratio of a steel member is an indicator showing the state of tallness of its form.

Slenderness Ratio of steel member is a division of its length to its section turning radius. More

slenderness ratio means longer length or smaller section, so the form of steel member is more

slim and weaker. Lesser slenderness ratio means shorter length or bigger section, so the form of

steel member is more rotund and stronger.

The slenderness ratio of a compression member shall be not more than 200 for those to be used

as the main post members, not more than 220 for compression members other than main post

members (excluding those used as auxiliary members) and not more than 250 for those used as

auxiliary members.

2.2.4 Minimum Thickness of Steel Plates The thickness shall be not less than 1 mm.

45

2.3 Strength of Steel Members and Bolts

Steel members and bolts to be used for a steel tower or an iron pole of overhead transmission lines shall have

the strength as specified in Table 16B.

Table 16B: Strength of Steel Members and Bolts

Classification of strength Strength

When σY≤ 0.7σB σY Tensile strength

When σY > 0.7σB 0.7σB

Compression strength σY

Flexural strength σY

When σY≤ 0.7σB σY / 3 Shearing strength

When σY > 0.7σB 0.7σB / 3

Bearing strength 1.65σY

0 < λk < Λ ( )( ) ( )( ) σ λ π σ λ π σY K K E Y K E Yk k0 1 2

2

− −⎡

⎣⎢

⎤

⎦⎥

Buckling strength Λ≤λk 1.5π2E / 2.2λk2

Where:

σY: Yield point strength of steel members and bolts

σB: Tensile strength of steel members and bolts

λk: Effective slenderness ratio ( = Lk / r )

Lk: Effective buckling length of steel members

r: Turning radius of a steel member cross section

E: Elastic modulus (20.6 × 102 N/m2)

Λ: ( )π σ15 2 2. .E K Y

K, K0, K1, K2: Refer to Table 16C.

Table 16C K, K0, K1, K2, for Table 16B

K K0 K1 K2

Structural members with little decentering (steel pipe,

cruciform section steel, etc.) 0.6 1 0 0.352

Structural members with some decentering (angle steel

used for a main post member, etc.) 0.5 0.945 0.0123 0.316

Structural members with significant decentering (angle steel

used for a web member with one side flange joint, etc.) (*) 0.3 0.939 0.424 0

(*) Note that the buckling strength shall be not more than 0.6σY for structural members with significant

decentering.

46

2.4 Strength of Foundation Components used for Steel Poles or Steel Towers

Foundation components of a steel pole or steel tower for overhead transmission lines shall have the

strength specified below:

a. Strength of Concrete

The strength of concrete at yield point shall be based on the design standard strength (4-week

strength; Fc) of concrete and conform to Table 16D.

Table 16D: Strength of Concrete

Kind of strength Strength of concrete [×106N/m2]

Compression strength Fc/2

Tensile strength Fc/20

Shearing strength Fc/20 and 0.74+1.5Fc/100

b. Bond Strength of Concrete

The bond strength of concrete at yield point shall be based on the design standard strength (4-

week strength; Fc) and conform to Table 16E.

Table 16E: Bond Strength of Concrete

[×106N/m2]

Member

Upper edge round

bar

Normal round bar Fixative joint

Round bar 6Fc/100 and not

more than 1.32

9Fc/100 and not more

than 1.99

6Fc/100 and not more than 1.32

Deformed

round bar

Fc/10 and not more

than 1.32+3Fc/75

3Fc/20 and not more

than 1.99+3Fc/50

Fc/10 and not more than

1.32+3Fc/75

Shaped steel 3Fc/100 and not more than 0.66

c. Strength of Shaped Steel, Flat Steel and Steel Bars

The strength of shaped steel, flat steel and steel bars at yield point shall conform to Table 16F.

47

Table 16F: Strength of Shaped Steel, Flat Steel and Steel Bars

Yield tensile strength

(N/mm2)

Yield compression strength

(N/mm2)

Round bar σY and not more than 234 σY and not more than 234

Diameter≥ 29 mm σY and not more than 294 σY and not more than 294

29 mm > Diameter > 25 mm σY σY Deformed

round bar

25 mm≥Diameter σY and not more than 322 σY and not more than 322

Others σY and not more than

0.7σB σY

σY: Strength of material at yield point

σB: Tensile strength of material

d. Strength of Bolts

The strength of bolts shall conform to Table 16B.

3. Wind Pressure Load

3.1 Wind Pressure Values

The wind pressure load shall be the value obtained by calculation based on the wind pressure specified in

the following Table 16G.

This shall not apply when calculation is made based on values obtained by a wind pressure (wind duct)

test using a wind at a velocity of not less than 32 m/s.

The wind receiving area shall be the vertical projected area of the structural member. For crossarms of a

concrete pole, an iron pole except a columnar pole, and a steel tower, the wind receiving area shall be the

vertical projected area of the front structures that receive the wind.

48

Table 16G: Wind Pressure to calculate the Wind Pressure Load

Subject to the wind pressure Wind pressure to 1 m2 of the vertical

projected area of the structural member (N)

Columnar pole 520

Triangle or rhombic pole 1,220

Square pole consisting of

steel pipes 970 Iron pole

Others 1,540

Columnar pole 520 Reinforced

concrete pole Square pole 1,290

Shaped steel tower 2,350 *

Steel pipe tower 1,340 *

Columnar pole 520

Supp

ortin

g st

ruct

ure

Steel tower Single

pole Hexagonal or

octagonal pole 970

Electrical wires forming multiple conductors

(limited to those in which two compositional

conductors are arranged horizontally and the

distance between such electrical conductors is

not more than 20 times their outer diameter)

610

Elec

trica

l co

nduc

tors

an

d ot

her w

ires

Others 680

Insulator device 900

1,030 when it is used as a single member Crossarms for an iron pole (limited to a columnar pole)

and a reinforced concrete pole 1,410 in other cases

* This value shall be applied to 115kV high-voltage towers which are less than 40m high.

3.2 Wind Pressure Load at an Oblique Wind When the wind blows to the electrical line at an angle of 60°, the wind pressure load in an assumed

normal load of a common type steel tower shall be that calculated by the wind pressure load multiplier

(in case of a square tower) in Table 16H.

49

Table 16H: Multiplier to Wind Pressure Load

Classification of wind pressure load

The multiplier to the wind pressure load when

the wind blows perpendicular to the electrical

line (in case of a square tower)

Shaped steel tower 1.6 Wind pressure

load to body Steel pipe tower 1.4

Wind

pressure

load to steel

tower Wind pressure load to cross arm

0.5 (for the wind pressure in the direction of

the electrical line)

Wind pressure load to wire 0.75

4. Loads on Supporting Structures and Safety Factors

Loads on supporting structures and safety factors shall satisfy the following items or shall have an equivalent

performance to these items.

4.1 Types and Combinations of Assumed Loads

The types and combinations of assumed loads to be used for calculating the strength of supporting

structures for overhead transmission lines shall conform to the following provisions.

The assumed loads on supporting structures shall be classified as the loads specified in Table 16I. The

combination of these loads on the supporting structures shall be in accordance with Table 16J depending

on the classification and type of supporting structures.

Table 16I: Classification of Assumed Loads on Supporting Structures

Type of Load Contents Symbol

Weight of the supporting structure Wt

Weight of the conductors and the ground wires and the accessories supported by the supporting structure Wc

Weight of the insulator strings and the fittings supported by the supporting structure Wi

A vertical component of the maximum tension of the conductors and the ground wires Va

Vertical loads

A vertical component of the maximum tension of the guy wires supporting the supporting structure, if any Ws

Wind pressure on the supporting structure under maximum wind velocity Ht

Wind pressure on the conductors and the ground wires supported by the supporting structure under the maximum wind velocity Hc

Horizontal transverse

loads

Wind pressure on the insulator strings and the fittings supported by the supporting structure Hi

50

A horizontal transverse component of the maximum tension of the conductors and the ground wires supported by the supporting structure and the guy wires supporting the supporting structure, if any

Ha Hs

A torsional load due to the unbalance of the maximum tension of conductors of any phase q

Wind pressure on the supporting structure under the maximum wind velocity Ht'

A horizontal longitudinal component of the maximum tension of the guy wires supporting the supporting structure, if any Ws'

The unbalance of the maximum tension of the conductors of all phases and the ground wires P1

The unbalance of the maximum tension of the conductors of any phase P2

Horizontal longitudinal loads

A torsional load due to the unbalance of the maximum tension of the conductors of any phase q1

Table 16J: Combination of Loads on the Supporting Structures

Design cases Combination of assumed loads

Vertical load Horizontal transverse

load

Horizontal

longitudinal load

Classifica-

tion of

supporting

structure

Type Load

condi-

tion

Wind

direction Wt Wc, Wi Va Ws Ht Hc, Hi Ha Hs q H’t P1 P2 q1 W's

Horizontal

transverse

Tension &

Suspen -

sion Type

Tower

Normal Horizontal

longitudinal

Horizontal

transverse

Concrete

pole

Steel pole Dead-end

Type Tower Normal

Horizontal

longitudinal

Horizontal

transverse/60°

Normal Horizontal

longitudinal

Horizontal

transverse

Tension &

Suspen-

sion Type

Tower Abnor-

mal Horizontal

longitudinal

Horizontal

transverse

Normal Horizontal

longitudinal

Horizontal

transverse

Steel tower

Single steel

pole Dead-end

Type Tower

Abnor-

mal Horizontal

longitudinal

51

Where:

Dead-end type: Supporting structure with a large unbalanced load in the horizontally

longitudinal direction, e.g. the first tower from a substation.

Abnormal Condition: An assumption for tower design where any one or two of conductors and

ground wires will be broken down

Notes: Circles " " indicate the assumed loads to be considered at the same time that

can combine together.

The wind direction that brings the bigger assumed load should be selected.

Where strung wires are arranged asymmetrically on the supporting structure, the assumed vertical

eccentric load shall be added to the load in Table 16J and the load by normal torsional load shall

also be added for the dead-end type.

4.2 Unbalanced Maximum Tension and so on

Unbalanced maximum tension and so on used in 4.1 shall conform to the following requirements:

4.2.1 The unbalanced maximum tension and torsional force shall conform to Table 16K.

Table 16K: Unbalanced Tension and Torsional Force

Unbalanced tension and torsional force Classification of

supporting structure

Type of supporting structure Assumed normal load Assumed abnormal load

Tension & Suspension Type

Tower No specification

Steel tower

Dead-end Type Tower

Horizontal longitudinal component of force of the unbalanced tension equal to the assumed maximum tension for each strung wire

Horizontal longitudinal component of force of the unbalanced tension and torsional force generated by cutting strung wires

Tension & Suspension Type

Tower No specification

Iron reinforced

concrete pole and iron pole Dead-end Type

Tower

Horizontal longitudinal component of force of the unbalanced tension equal to the assumed maximum tension for each strung wire

No specification

52

4.2.2 For steel towers, the strung wires shall be cut according to the following requirements, depending on

the total number of phases of electrical conductors (which mean phases for each circuit. The same

shall apply hereafter).

a. The overhead ground wire shall not be cut at the same time as the electrical conductors and

only one wire shall be cut;

b. Where the total number of phases of electrical conductors is not more than twelve (12), one

phase that maximizes the stress generated in each structural member (two electrical

conductors from one phase in case of multiple conductors for steel towers other than dead-

end type);

c. Where the total number of phases of electrical conductors is over twelve (12) (excluding the

case specified in the following Item d.), two phases in different circuits that maximize the

stress generated in each structural member (two electrical conductors from one phase in case

of multiple conductors for steel towers other than dead-end type);

d. Where electrical conductors are arranged so that nine or more phases are in a longitudinal

row and two phases are in a transverse row, one of the top six phases in the longitudinal row

(two electrical conductors from one phase in case of multiple conductors for steel towers

other than dead-end type) and one phase from the other phases (two electrical conductors

from one phase in case of multiple conductors for steel towers other than dead-end type) that

maximize the stress generated in each structural member.

4.2.3 The unbalanced tension generated by cutting the strung wire shall be equal to the assumed maximum

tension.

Provided，however, that the unbalanced tension may be 0.6 times the assumed maximum tension if,

depending on the mounting method of the strung wire, the supporting point of the strung wire shifts

when the wire is cut or the strung wire slides at the supporting point.

4.3 Safety Factor of Supporting Structure

The yield strength of the structural members of reinforced concrete poles, iron poles and steel towers

used for overhead transmission lines shall satisfy the safety factor listed in Table 16L for the assumed

loads specified in 4.1 to 4.2.

Table 16L: Safely Factors of Supporting Structures

Classification of supporting structure Load condition Safety factor

Reinforced concrete pole

Iron pole Assumed normal load 2.0

Steel tower Assumed normal load 1.5

53

Assumed abnormal load 1.0 (1.5 for crossarms)

5 Loads on Foundations of Supporting Structures and Safety Factors

5.1 Loads on the Foundation of a Supporting Structure

The loads applied to the foundation of a supporting structure for overhead transmission lines shall be

calculated from combinations of the assumed loads of the supporting structure specified in paragraph 4

and the resulting maximum values shall be the assumed normal and abnormal loads for the foundation.

5.2 Safety Factor of the Foundation

The safety factor of the foundation of a supporting structure for overhead transmission lines shall

satisfy the value listed in Table 16M for its yield strength.

Table 16M: Safety Factors of the Foundations

Safety factor Classification of supporting structure

Assumed normal load Assumed abnormal load

Reinforced concrete pole and iron pole 2.0 -

Steel tower 2.0 1.33

5.3 Treatment of the Weight of the Foundation

The weight of the foundation used for calculating the safety factor shall be treated in accordance with

the following provisions:

a. For a foundation that is subject to a lifting load, not more than two-thirds of the weight of

the foundation (or the weight of the foundation of a steel tower to an abnormal load) may be

included in the lift bearing power.

b. For a foundation that is subject to a compressive load, the weight of the foundation shall be

included in the compressive load.

Article 32: Design of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines

1. Safety Factor of Fittings for Conductors and/or Ground Wires of Overhead High-voltage Lines

1.1 The safety factor for the tensile strength (the maximum tensile strength or breaking strength) of

fittings of conductors and ground wires for overhead high-voltage lines shall be 2.5 or more.

1.2 The safety factor mentioned in 1.1 shall be obtained as follows:

a. Tension insulator device (insulator device that anchors electrical conductors)

54

[Safety factor] = [Tensile break strength] / [Assumed maximum tension at a support point];

b. Suspension insulator device (Insulator device from which electrical conductors are hung)

[Safety factor] = [Tensile break strength] / [Composite load of vertical load and horizontal

transverse load];

c. Supporting insulator device

[Safety factor] = [Bending break strength] / [Horizontal transverse load or vertical load applied

perpendicular to the axis of the insulator device].

2 Mechanical Strength of Insulators for Overhead Transmission Lines

2.1 Assumed Load

The assumed loads to be used for calculating the strength of insulator devices for overhead transmission

lines shall conform to the following requirements.

a. Vertical Load

The vertical load shall be the sum of the weight of electrical conductors, the weight of insulator

devices and the vertical component of the force generated by the assumed maximum tension of

the electrical conductors.

b. Horizontal Transverse Load

The horizontal transverse load shall be the sum of the wind pressure loads of electrical

conductors and insulator devices and the horizontal component of load generated by the assumed

maximum tension of the electrical conductors. The wind pressure loads shall be calculated based

on the values listed in Table 16G.

c. Assumed Maximum Tension of Conductors

The assumed maximum tension of conductors shall be the tension of the transmission

conductor under the composite load of the vertical load generated by the weight of the electrical

conductor, and the horizontal load generated by the horizontal wind pressure stipulated in Table

16G at the average temperature in the area.

Article 33: Protection against Lightning for Overhead High-voltage Lines

The following measures shall be taken for overhead high-voltage lines to decrease the number of electrical

faults and to protect equipment from damage caused by the faults.

a. Installation of ground wires for overhead high-voltage lines;

b. Installation of arcing horns for both ends of insulator assemblies of overhead high-voltage lines;

c. Installation of armor rods to wrap conductors in a clamp of suspension insulator assemblies of

overhead high-voltage lines.

55

Article 34: Bare Conductors of Overhead High-voltage Lines

1. Vibration Dampers

An appropriate type and number of dampers shall be installed to prevent fatigue of bare conductors and

ground wires for overhead high-voltage lines due to their aeolian vibration.

2. Connection

In case bare conductors and ground wires are jointed with each other or with insulated conductors or cables,

the connection shall conform to the following requirements in addition to Article 26 of these SREPTS.

a. Bare conductors and ground wires shall be connected with compression type sleeves or

compression type devices.

b. The tensile strength of connection of bare conductors and ground wires shall be not less than 95 %

of the tensile strength of the connected bare conductors and ground wires. This requirement,

however, shall not be applied to cases where the maximum tension to be designed is substantially

less than the ultimate strength of the bare conductors and ground wires such as jumper conductors,

the end span to substations and others.

Article 35: Clearance between Bare Conductors and Supporting Structures of Overhead High-voltage

Lines

Clearance between bare conductors and supporting structures, arms, guy wires and/or pole braces of

overhead high-voltage lines shall be as follows. The clearances shall be secured, in any cases where the

maximum swing of conductors under the maximum wind velocity to be designed.

Table 17: Clearance between Bare Conductors and Supporting Structures

Nominal Voltage Clearance

115kV Not less than 0.70m


Clearance between ground wires and the nearest conductor in the same span shall be larger at any point in the

span than the clearance of the supporting point at both sides of the span.

Article 36: Height of Overhead High-voltage Lines

The height of conductors of overhead high-voltage lines shall be as follows:

56

1. Height in Urban Areas

Height of conductors of overhead high-voltage lines in urban areas shall be not less than the value

calculating by adding 0.060 m to a base height 6.5m for every 10kV over 35kV.

Table 18A: Height in Urban Areas

Nominal Voltage Height



2. Height in Areas Where Third Persons Hardly Approach

The height of conductors of overhead high-voltage lines in areas where third persons hardly approach shall be

not less than the value calculated by adding 0.06 m to a base height of 5.5m for every 10kV over 35kV.

Table 18B: Height in Areas Where Third Persons Hardly Approach




3. Height over Roads and/or Railways

The height of conductors of overhead high-voltage lines crossing over roads and/or railways shall be not less

than the value calculated by adding 0.060 m to a base height of 13m for every 10kV over 35kV.

Table 18C: Height over Roads and/or Railways




4. Height over Rivers and/or Seas

The height of conductors of overhead high-voltage lines crossing rivers and/or seas shall be as follows:

57

Table 18D: Height over Rivers and/or Seas

At places with no vessel passage At places with vessel passage

From the highest water level From the highest point of vessels on the

highest water level(*1)

Not less than the value calculated by adding

0.06 m to a base height of 5.5m for every 10kV

over 35kV

Not less than the value calculated by adding

0.06 m to a base height of 3m for every 10kV

over 35kV

Nominal Voltage Height Nominal Voltage Clearance

115kV Not less than 6.0m 115kV Not less than 3.5m

230kV Not less than 6.7m 230kV Not less than 4.2m

(*1) The highest point of vessels shall be decided taking into account any future possible changes.

5. Note

All the heights described above shall be secured in any cases of the maximum sagging of conductors in the

maximum temperature to be designed.

Article 37: Clearance between Overhead High-voltage Lines and Other Facilities or Trees

1 Generals

The clearance between each conductor of overhead high-voltage lines and other facilities or trees shall be as

follows:

a. Clearance to Other Facilities

The clearance between each conductor of overhead high-voltage lines and other facilities shall be

not less than the value calculated by adding 0.06 to a base height of 3m for every 10kV over 35kV.

Table 19A: Clearance to Other Facilities




58

b. Clearance to Trees

The clearance between each conductor of overhead high-voltage lines and trees shall be not less

than the value calculated by adding 0.06 m to a base height of 2m for every 10kV over 35kV.

Table 19B: Clearance to Trees




c. Note

The clearances described above shall be secured in any cases of the maximum sagging of

conductors in the maximum temperature and/or the maximum swing of conductors under the

maximum wind velocity to be designed.

Figure 7: Direct Proximity

Other facilities

Clearance

Support

Clearance

<Condition of Conductors> -At the maximum temperature -Maximum swing angle under the maximum

wind speed

59

2 Proximity to and Crossing with Buildings

2.1 230kV Overhead High-voltage Line

Overhead transmission conductors with a nominal voltage 230kV shall be installed not less than 3

meters away in a horizontal distance above or to the side of buildings.

Figure 8: Proximity to Buildings (230kV)

2.2 115kV Overhead High-voltage Line

Overhead transmission conductors with a nominal voltage of 115kV shall be installed not less than

6 meters from the top of buildings when the 115kV overhead high-voltage line is adjacent laterally

within 3m or crossing with buildings.

Support

Building

Horizontal distance: Not less than 3m

60

Figure 9: Crossing with Buildings (115kV)

3. Proximity to and Crossing with Medium-voltage Lines and High-voltage Lines

The clearance between each conductor of overhead high-voltage lines and other medium-voltage lines or

high-voltage lines shall be not less than the value calculated by adding 0.06m to a base height of 2m for every

10kV over 35kV.

Table 20: Clearance between Conductors

Nominal Voltage[kV] Clearance[m]

115 Not less than 2.5 Clearance (Ll*)

230 Not less than 3.2

* Refer to Figure 10.

Support

Building

Lb: not less than 6 m Lb: not less than 6m

3 m 3 m

Building

61

Figure 10: Proximity and Crossing with Medium-voltage Lines and High-voltage Lines

Article 38: Prevention of Danger and Interference due to Electrostatic Induction and Electromagnetic

Induction

1. Electrostatic Induction

High-voltage lines shall be installed to prevent danger to persons and/or interference on communication lines

installed near the high-voltage lines caused by electrostatic induction, taking appropriate measures including

the following items a, b and Article 28 of these SREPTS into consideration.

a. The electrical field caused by overhead high-voltage lines shall be 3kV/m or less at 1 m above the

ground surface, except for overhead high-voltage lines in places where third persons hardly

approach, such as in mountains, on farming land and so on.

b. Conductive materials on the surface of the buildings under overhead high-voltage lines shall be

grounded with the Class D grounding in accordance with Article 22 of these SREPTS.

2. Electromagnetic Induction

High-voltage lines shall be installed to prevent danger to persons and/or interference on communication lines

caused by electromagnetic induction on the low voltage lines and/or communication lines installed near the

high-voltage lines, taking appropriate measures including Article 28 of these SREPTS.

Medium-voltage or high-voltage line

Support

L1

62

Article 39: Surge Arresters

1. Generals

Surge arresters shall be installed at the appropriate places on electrical lines.

2. Installation of surge arresters

2.1 Installation Points for Surge Arresters

In high-voltage and medium-voltage electrical circuits surge arresters shall be installed at the points

listed below or at locations close to such points, in order to prevent damage to be electrical

equipment installed in electrical circuits in the power stations, substations and switching stations

and high-voltage and medium-voltage users’ sites, by over-voltage.

However, the same shall not apply in cases where there is no risk of damage to such electrical

equipment.

a. Receiving and outgoing points on overhead electrical lines in the power stations,

substations and switching stations;

b. Receiving points on the high-voltage and medium-voltage users’ sites to which power is

supplied from high-voltage and medium voltage overhead electrical lines;

c. Locations where there is a risk that the protective effects of surge arresters installed in

accordance with the above provisions may not be achieved.

Figure 11: Installation Points for Surge Arresters

Substation

User

230kV, 115 kV 22kV

UsersUsers

Users

230V, 400V

230V, 400V

Surge arrester

Power station, substation or

switching station

63

2.2 Grounding of Surge Arresters

Grounding of surge arresters shall be installed in accordance with Article 22 and 23 of these

SREPTS.

The grounding resistance provided for surge arresters in high-voltage and medium-voltage


voltage users’ sites shall be as much lower than 10 Ω as possible in order to prevent hinder to the

functions of the surge arrester.

64

CHAPTER 4

MEDIUM AND LOW-VOLTAGE

DISTRIBUTION FACILITIES

65

Article 40: Supporting Structures

1. Loads on Overhead Distribution Lines

Supporting structures of overhead medium-voltage and low-voltage lines shall be designed taking into account

the loads shown in Table 21A.

Table 21A: Kinds of Loads

Type of Load Contents

Weight of supporting structures

Weight of the conductors and the ground wires and the accessories supported by

the supporting structure

Weight of the insulating devices, the crossarms and the distribution equipment

supported by the supporting structure

Vertical loads

A vertical component of the maximum tension of the guy wires supporting the

supporting structure, if any


Wind pressure on the conductors and the ground wires supported by the

supporting structure under the maximum wind velocity

Wind pressure on the insulator, the crossarms and the distribution equipment

supported by the supporting structure under the maximum wind velocity

Horizontal

transverse loads

A horizontal transverse component of the maximum tension of the conductors

and the ground wires supported by the supporting structure and the guy wires

supporting the supporting structure, if any


Horizontal

longitudinal loads

A horizontal longitudinal component of the unbalanced maximum tension of the

conductors and the ground wires supported by the supporting structure and the

maximum tension of the guy wires supporting the supporting structure, if any

By calculating, firstly, the load when wind pressure is applied in a horizontal transverse direction to the

distribution line, and secondly, the load when wind pressure is applied in the horizontal longitudinal direction

of the distribution line, the one of these two loads which generates greater stress on the structural member

shall be adopted for the assumed normal load.

2. Safety Factor of Foundations of Supporting Structures

- The safety factor of the foundations of supporting structures for low-voltage lines shall be 2 or more

to the wind pressure.

66

- The safety factor of the foundations of supporting structures for medium-voltage lines shall be 2 or

more to the load prescribed in Table 21A.

- If wooden poles, iron-poles and iron-reinforced concrete poles are installed at other than soft ground

in accordance with Table 21B, this article may not be applicable.

Table 21B

Design load of

poles Length of poles Setting depth Span

15m or less 1/6 of overall length or more

Woo

den

pole

---- More than 15m,

and 16m or less 2.5m or more

Medium-voltage

lines in an urban

area: Not more

than 75m


Iron

pol

e

---- More than 15m,



More than 15m,


Iron

-rein

forc

ed

conc

rete

pol

e

6.5kN or less

More than 16m,


Low-voltage lines

in an urban area:

Not more than

40m

Other: Not more

than 150m

3. Strength of Iron-reinforced Concrete Pole

- Iron-reinforced concrete poles for low-voltage lines shall have the strength to withstand wind

pressure.

- Iron-reinforced concrete pole for medium-voltage lines shall have the strength to withstand the load

prescribed in Article 31 of these SREPTS.

- Iron-reinforced concrete pole shall have the strength to withstand two times of the design load.

4. Safety Factor of conductors and supporting structures

4.1 Conductor

A safety factor of 2.5 or more shall be applied to the tensile strength (ultimate tensile strength; breaking

strength) of overhead distribution conductors and overhead ground wires.

67

4.2 Supporting Structure

(1) Supporting structures for overhead low-voltage lines shall have the strength to withstand a

load of 1.2 times the wind pressure for wooden poles, and a load equal to the wind pressure

for others.

(2) Wooden poles to be used as the supporting structures for overhead medium-voltage lines

shall be installed in accordance with the following items:

a. The safety factor against a wind pressure shall be 1.5 or more; and

b. The thickness shall be not less than 12 cm in diameter at the top end.

(3) Iron-reinforced concrete poles and iron poles to be used as supporting structures for

overhead medium-voltage lines shall have the strength to withstand the assumed normal

load.

5. Reference Wind Velocity

Reference wind velocity used in the calculation of wind loads on overhead distribution lines shall be as

follows:

Table 21C: Reference Wind Velocity

Yearly maximum of 10-minute average wind velocity

(50 year return period) 32m/sec

In the following circumstances, the above reference wind velocity shall be changed:

a. When sufficient observed wind velocity data have been accumulated.

b. When greater reliability is particularly needed.

c. When a terrain has the effect to decrease the wind velocity.

6. Reinforcement for Supporting Structures by Guys

Supporting structures shall be guyed to share strength with the guys according to Table 21D. In such case, the

strength of the supporting structure itself shall be such that it bears at least half of the wind load.

6.1 Installation and Safety Factor of Guys

a. Installation of Guys

68

Guys shall be installed in order to reinforce the foundation of a supporting structure if the calculated

result of the safety factor of supporting structure’s foundation is less than 2.0 under the following

conditions.

Table 21D: Conditions of Installation of Guys

Conditions Installation method Safety factor

of the guy

a. Supporting

structures lacking strength against

wind pressure

Guys that withstand wind pressure shall be

installed at right angle to the lines. 2.5 or more

b. Supporting structure of which

spans on both sides are too

different

Guys that withstand the force caused by

unbalanced tension shall be installed on both

sides in the direction of the line.

1.5 or more

c. Supporting structure of which lines

on both sides make an angle of

more than 5 degrees

Guys that withstand the force caused by the

assumed maximum tension of each line shall

be installed at the opposite side of the line.

d. Supporting structure which

supports the end of a line

Guys that withstand the assumed maximum

tension of the line shall be installed at the

opposite side of the line.

1.5 or more

b. Section near the Ground of the Guy

For the section near the ground, that is, from the underground portion of the guy to 30cm above the

ground, a galvanized iron rod or similar rod equal or superior to it in strength and corrosion

resistance shall be used.

c. Foundation of the Guy

The guy anchor shall be installed firmly so that it can adequately bear the tensile load from the guy. A

guy anchor installed with a supporting structure shall be of such a material that it hardly corrodes.

d. Globe Insulator

If a guy is installed on an overhead distribution line that is in danger of touching an electrical

conductor, a globe insulator shall be inserted in the upper part of the guy.

A globe insulator, however, need not be inserted if the guy is installed on a low-voltage overhead

distribution line in a place other than a rice field or other swamp area.

69

e. Height of Guy

A guy crossing a road shall have a height of not less than 6.5 m from the road surface. If this is

impossible for technical reasons, a height of not less than 4.5m (not less than 2.5m, if a sidewalk) is

allowed if there is no danger of interfering with traffic.

f. Strut

A strut that has equivalent or higher effect than a guy can be substituted for a guy.

Article 41: Overhead Medium-voltage and Low-voltage Lines

1. Cables for Overhead Lines

a. When cables are used for overhead lines, the cables shall be installed using messenger wires or

other appropriate measures so that they bear no tensile strength. The messenger wires shall be

installed in accordance with the provision of Article 32 of these SREPTS.

b. When cables are installed along a building or another object, the cables shall be supported so that

they are not damaged by contacting the building or the object.

2. Connecting Methods of Overhead Conductors

The tensile strength of the conductors shall not be reduced by 20% or more, when electric conductors are

connected. If the tension on the conductors is distinctly less than the general tensile strength of conductors,

this may not apply.

3. Branching of Overhead Lines

Branching of overhead lines shall be made at the supporting point of the lines. If branching can be done in a

way that does not to inflict tension on the conductor at the branch point, this may not be applicable.

Article 42: Mechanical Strength of Insulators

1. Generals of Mechanical Strength of Insulators

The insulator to support medium-voltage lines shall be installed in such a manner that it has sufficient strength

to attain the safety factor of at least 2.5 based on the assumption that the following loads are exerted on the

insulators.

a. For the insulators to anchor lines, the load is the assumed maximum tension of the lines.

b. For the insulators to support lines, the load is the horizontal lateral load or vertical load exerted

perpendicular to the axis of the insulators.

70

2. Safety factor of Insulators

The safety factor of insulators for medium-voltage lines shall be calculated using the following equations.

a. Tension insulator (Insulator that anchors electrical conductors)

[Tensile break strength]

[Safety factor] =

[Assumed maximum tension of the lines]

b. Supporting insulator

[Tensile break strength]

[Safety factor] = [Horizontal transverse load or vertical load applied perpendicular to the

axis of the insulator device]

3. Assumed Load

The assumed loads to be used for calculating the strength of insulator for medium-voltage lines shall conform

to the following requirements.

a. Vertical load

The vertical load shall be the sum of the weight of electrical conductors and the weight of insulator

devices.

b. Horizontal transverse load

The horizontal transverse load shall be the sum of the wind pressure loads of electrical conductors

and insulator devices and the horizontal component of a load generated by the assumed maximum

tension of the electrical conductors. The wind pressure loads shall be calculated based on the

values listed in Table 22.

Table 22: Wind Pressure Loads

Segment of an object receiving wind pressure Wind pressure to 1m2 of the vertical projected

area (Pa)

Electrical conductor and other strung conductor 680

Insulation device 900

*The wind pressures are obtained from 32m/s wind velocity as same as Table 21C.

71

4. Assumed Maximum Tension of the Lines

The assumed maximum tension of the lines shall be the tension of the medium-voltage line conductor under

the composite load of:

a. The load generated by the weight of the electrical conductor, and

b. The horizontal load generated by the horizontal wind pressure stipulated in Table 22.

Article 43: Medium-voltage/Low-voltage (MV/LV) Transformers

MV/LV transformers, including medium-voltage conductors other than cables, shall be installed so that they

are not in danger of electrical shock using either of the following methods.

1. MV/LV transformers shall be installed in an exclusive cabin that is locked.

2. MV/LV transformers shall be installed at a height of not less than 5.0m above the ground in order

that persons can not touch them easily.

3. Appropriate fences shall be installed around the MV/LV transformers in order that persons can not

touch them easily and warning signs to indicate the danger shall be displayed. Otherwise MV/LV

transformers, the charged parts of which are not exposed shall be installed so that persons can not

touch them easily.

Article 44: Installation of Distribution Transformers for Single Wire Earth Return (SWER) Systems

1. Grounding Arrangement for SWER

Grounding on the primary side of distribution transformers for SWER shall be installed by the following

methods, in order to avoid risk of danger to persons, domestic animals and other facilities due to the potential

difference between the grounding conductor and the ground caused by load current, when any failure occurs.

a. The grounding resistance shall be not more than 5ohms.

b. The cross-sectional areas of grounding conductors shall be not less than 16mm2.

c. The grounding conductors placed up to a depth of 75cm underground or up to a height of 2.0 m

above ground shall be covered by a synthetic resin pipe or another shield of equivalent or higher

insulating effect and strength.

d. The grounding for SWER installed on the primary side of a distribution transformer and the Class

B grounding for it shall be completely separated to keep the safety of low voltage line system.

2. Load Current of Distribution Transformers

The load current in any earth-return circuits shall be not more than 8 amperes.

72

3. Isolating Transformer

SWER circuits shall be supplied from double-wound transformers (isolating transformers).

4. Safety of Third Persons

Warning signs to alert third persons’ attention shall be installed near the grounding point.

Article 45: Protective Devices

1. Installation of Medium-Voltage Over-current Circuit Breakers

a. On medium-voltage lines, an over current circuit breaker shall be installed at the outgoing point of a

substation or similar location and on the primary side of a transformer.

b. Over current breakers for short circuit protection shall have the ability to break the short circuit

current that passes the breakers.

2. Installation of Medium-Voltage Ground Fault Circuit Breakers

A ground fault breaker that breaks circuit automatically when an earth fault happens in the lines shall be

installed at an outgoing point of substation or similar locations.

3. Installation of Surge Arresters

To prevent electrical equipment from being damaged by lightning, surge arresters shall be installed at the

places of lines stated below or their surrounding areas. If electric power facilities are not damaged by lightning,


a. A lead-out of overhead line from power station, substation, and equivalent places.

b. The connecting point of overhead medium-voltage lines with a main transformer.

4. Exceptions to Installation of an Over Current Breaker for Medium-voltage and Low-voltage Lines

No over current circuit breaker shall be installed at the following places:

a. Grounding conductor of grounding work.

b. Neutral conductor of an electrical conductor. An over-current circuit breaker, however, may be

installed if all the poles are shut off simultaneously.

c. Grounding conductor of a low-voltage overhead electrical conductor whose circuit is provided with

class B grounding work in part.

73

Article 46: Height of Overhead Medium-voltage and Low-voltage Lines

1. Regulations for Medium and Low-voltage Overhead Distribution Conductors

The height of medium and low-voltage overhead lines shall be no less than the values in the following table:

Table 23: Height of Medium and Low-Voltage Overhead Lines

(Unit: meter)

Medium-voltage

Urban area Low-voltage

Cable Others Other area

Crossing a road 6.5 8.0 8.0 6.5

Others 5.5 5.5 6.5 5.5

2. Urban Areas to be Included

The following areas shall be included in the urban area.

a. Area

- Phnom Penh city and other cities

- Provincial towns

b. Road

-The National Road

- The Provincial Roads

3. Exclusions for Road Crossings

The conductor is not regarded as crossing a road in the followings:

- The road is so narrow that cars can not pass through it.

- The road is on private land.

4. Mitigation of Height for Low-voltage Conductors

The minimum height of the low-voltage conductor is mitigated up to 4.0 m on the place other than a road.

Furthermore, the minimum height of the low-voltage conductor is mitigated up to 3.0 m on the following

conditions:

- The licensee owning the distribution line is a small licensee in the area other than urban areas;

- The insulation of the conductor(s) must be always kept in good condition;

- Vehicles including carts never pass under the line.

74

Article 47: Clearance between Overhead Medium-voltage and Low-voltage Lines and Other Objects

1. Clearance between Overhead Lines and Buildings/Plants

The minimum clearance between a line and another object shall be the values shown in the Table 24A.

Table 24A: Clearance between Overhead Lines and Other Objects

(Unit: meter)

Low-voltage Medium-voltage

Bare conductor - 3.0

Insulated conductor 2.0 2.5 With the possibility for

persons to climb on

Cable 1.0 1.2


Insulated conductor 1.2 1.5

Up

side

prox

imity

Others

Cable 0.4 0.5


Insulated conductor 1.2 1.5

Stru

ctur

es o

f bui

ldin

gs

Lateral and downside proximity

Cable 0.4 0.5


Insulated conductor Shall not contact directly Plants

Cable Shall not contact directly

Low-voltage cable including ABC (Aerial Bundle Conductor) type cable may be installed directly on a wall of a

building by using a clip and clamp in such a way that in normal circumstances a person cannot reach the cable.

2. Clearance between Overhead Distribution Lines and a Road

When a supporting structure is installed below a road, the minimum clearance between a line and a road shall

be the values shown in Tables 24B and 24C.

75

Table 24B: Clearance between a Line and a Road on a Bank

(Unit: m)

Type of wire Low-voltage Medium-voltage Bare conductor Do not install 3.0

Insulated conductor 3.0 3.0 Direct proximity

Cable 3.0 3.0

Bare conductor Do not install 3.0 Insulated conductor 1.0 1.5 Lateral proximity

Cable 1.0 1.2

* If the lateral proximity is equal to the direct proximity, the lateral proximity required the same value as the

direct adjacency.

* If the lateral proximity is equal to the direct proximity, the lateral proximity required the same value

as the direct proximity.

Figure 12: Explanation of Direct Proximity and Lateral Proximity (Road on a Bank)

Road on a bank

Direct proximity

Height

Lateral proximity

Road

Lateral proximity Height

Direct proximity

76

Table 24C: Minimum Clearance between a Line and an Overpass

(Unit: m)

Type of wire Low-voltage Medium-voltage

Bare conductor Do not install Direct proximity:3.0

Insulated conductor Direct proximity:3.0

or Lateral proximity:1.0

Direct proximity:3.0

or Lateral proximity:1.5 Upper

access

Cable Direct proximity:3.0


Direct proximity:3.0


Bare conductor Do not install Lateral proximity:3.0

Insulated conductor Direct proximity:0.6 Direct proximity:1.5 Lower

access Cable Direct proximity:0.3 Direct proximity:0.5

Figure 13: Explanation of Direct Proximity and Lateral Proximity (Overpass)

Overpass

Lower Access

Lateral proximity

Direct proximity

Overpass

Lateral proximity

Direct proximity

Upper Access

77

Article 48: Proximity and Crossing of Overhead Medium-voltage and Low-voltage Lines

1. Multiple Medium-voltage Line

When a medium-voltage line is installed adjoining or crossing other medium-voltage lines, the clearance

between the two medium-voltage lines shall be not less than 2.0m. If one is a cable and the other is a cable or

an insulated conductor, the clearance shall be not less than 0.5m.

Above requirements shall be also applied, when two or more medium-voltage lines are installed at the same

supporting structure.

2. Medium-voltage Lines and Low-Voltage Lines

When a medium-voltage line and a low-voltage line are installed so that they adjoin or cross each other, they

shall be installed in the following manners.

- The medium-voltage line shall not be installed under the low-voltage lines. If the medium-voltage line

maintains a horizontal clearance of not less than 3.0m from the low-voltage line, and the low-voltage

line does not come in contact with the medium-voltage line when the support structure of the low-

voltage line collapses, this may not be applicable.

- The clearance between the medium-voltage line and the low-voltage line shall be not less than 0.5m

when the medium-voltage line is a cable, not less than 1.0m when it is an insulated conductor, and not

less than 2.0m when it is a bare conductor.

- The medium-voltage line shall not cross under the low-voltage line. If the medium-voltage line is a

cable and the clearance between the medium-voltage line and the low-voltage line is not less than 0.5m,


3. Multiple Low voltage Lines

When a low-voltage line is installed adjoining or crossing other low-voltage lines, the clearance between the

two low-voltage lines shall be not less than 0.6m. When one is a cable and the other is a cable or an insulated

conductor, the clearance shall be not less than 0.3m.

Above requirements shall be also applied, when two or more low-voltage lines are installed at the same

supporting structure.

4. Medium-voltage Lines and Communication Lines

When a medium-voltage line is installed adjoining or crossing a communication line, the medium-voltage line

shall be installed in the following manners.

- The medium-voltage line shall not be installed under the communication line. If the medium-voltage

line maintains a horizontal clearance of not less than 3.0m from the communication line, and the

communication line does not come in contact with the medium-voltage line when the support

structure of the communication line collapses, this may not be applicable.

78

- The clearance between the medium-voltage line and the communication line shall be not less than

0.5m when the medium-voltage is a cable, not less than 1.0m when it is an insulated conductor, and

not less than 2.0m when it is a bare conductor.

- The medium-voltage line shall not cross under the communication line. If the medium-voltage line is

a cable and the clearance between the medium-voltage line and the communication line is not less

than 0.5m, this may not be applicable.

5. Low-voltage Lines and Communication Lines

When a low-voltage line is installed adjoining or crossing a communication line, the low-voltage line shall be

installed in the following manners.

- The low-voltage line shall not cross under the communication line. If other methods are not

technically realistic, this may not be applicable.

- The clearance between the low-voltage line and the communication line shall be not less than 0.3m

when the low-voltage line is a cable, and not less than 0.6m when conductor is insulated.

79

Specific Requirements for Thermal Power Generating Facilities

80

Specific Requirements for Thermal Power Generating Facilities

CONTENTS

CHAPTER 1

Introduction


Article 2: Purpose



Article 5: Facilities regulated in this Specific Requirements

CHAPTER 2

Requirements for all types of Thermal Generating Facility

Article 6: Prevention of Electric Power Disasters from the Facility


Article 8: Requirements related to the Fuel

Article 9: Requirements related to the Handling of Chemical Materials

Article 10: Requirements related to the Natural Disasters

Article 11: Requirements related to the Operation of Generating Facility with Power System

Article 12: Requirements related to the Environment

Article 13: The Life of Electric Power Facilities

Article 14: Requirements related to the design of Electric Power Facilities

Article 15: Requirements related to the Technical Document of Electric Power Facilities

Article 16: Requirements related to the Grounding

CHAPTER 3

Requirements for Steam Turbine Generating Facility

Article 17: Steam Turbine Generating Facility

PART 1

Boiler

Article 18: Requirements for Materials of Boiler and its Accessories

Article 19: Requirements for Structure of Boiler and its Accessories

Article 20: Safety Valve for Vessels and Tubes of the Boiler

Article 21: Feed Water System of Boiler

81

Article 22: Water Feeding and Steam Outpouring of Boiler

Article 23: Monitoring the Running Condition of Boiler and Safety and Alarm System

PART 2

Steam Turbine

Article 24: Requirements for Materials of Steam Turbine and its Accessories

Article 25: Mechanical Strength of Structure of Steam Turbine and its Accessories

Article 26: Bearings of Steam Turbine

Article 27: Governance of Turbine Speed

Article 28: Requirements to Alarm and to Stop the Turbine in Emergency Case

Article 29: Monitoring the Condition of Turbine Operation

Article 30: Reviewing the Safety of Steam Turbine and its Accessories

CHAPTER 4

Requirements for Gas Turbine Generating Facility

Article 31: Gas Turbine Generating Facility

Article 32: Requirements for Materials of Gas Turbine and its Accessories

Article 33: Mechanical Strength of Structure of Gas Turbine and its Accessories

Article 34: Bearings of Gas Turbine


Article 36: Emergency Alarm and Stop Devices

Article 37: Monitoring and Alarm Systems

Article 38: Reviewing the Safety of Gas Turbine

Article 39: Requirements for Gas-Turbine Combined Cycle and its Accessories

CHAPTER 5

Requirements for Internal Combustion Engine

Article 40: Internal Combustion Engine

Article 41: Requirements for Materials of Internal Combustion Engine

Article 42: Mechanical Strength of Structure of Internal Combustion Engine

Article 43: Bearings of Internal Combustion Engine

Article 44: Governance of Internal Combustion Engine Speed

Article 45: Emergency Stop and Alarm Devices

Article 46: Overpressure Protection Devices


82

CHAPTER 6

Requirements for Generators

Article 48: Protection of Generators

Article 49: Electrical Equipment

Article 50: Cables in Thermal Power Plants

Article 51: Installation of Hydrogen Cooling Type Generators

Article 52: Control Systems

CHAPTER 7

Transitional Provisions

Article 53: Transitional Provisions for Small and Medium Licensees



Article 56: Safety Measures for Fuel and Chemical Materials


Article 58: Requirements for Operation

Article 59: Safety and Technical Training

83

CHAPTER 1

Introduction

84

CHAPTER 1

Introduction


In this Specific Requirements of Electric Power Technical Standards, unless the context otherwise requires,

the following terms shall have the meanings assigned to each term:

1. EAC

“EAC” is the acronym for the Electricity Authority of Cambodia.

2. Electrical Line

“Electrical Line” means the part of electric power facilities used to transmit or supply electricity,

which connects power stations, substations, switching stations and user’s sites, and includes lines and

associated protective devices and switchgears.

3. Electric Power Facility

“Electric Power Facility” means generating facilities, substations, switching stations, electrical lines,

and dispatching centers, including equipment, buildings, dam, waterways, fuel storage yards, ash

disposal areas, etc.

4. Electrical Equipment

“Electrical Equipment” means electrically-charged facilities.

5. GREPTS

“GREPTS” is the acronym for the General Requirements of Electric Power Technical Standards of

the Kingdom of Cambodia.

6. IEC

“IEC” is the acronym for the International Electrotechnical Commission.

7. ISO

“ISO” is acronym of International Organization for Standardization.

8. Licensee

“Licensee” means an electric power service provider who has been issued a license by the EAC.

9. SREPTS

“SREPTS” is the acronym for the Specific Requirements of Electric Power Technical Standards of

the Kingdom of Cambodia.

85

10. The Technical Standards

“The Technical Standards” means The Electric Power Technical Standards in the Kingdom of

Cambodia.

Article 2: Purpose

This Specific Requirements of Electric Power Technical Standards for Thermal Power Generating Facilities

prescribes the basic requirements necessary to regulate the existing and the planned thermal power generating

facilities in the Kingdom of Cambodia. The requirements in this standard document are mainly for facility

security and safety operation of the most important parts for thermal generating facilities.


All thermal power generating facilities in the Kingdom of Cambodia shall be in accordance with the

requirements prescribed in this Technical Standard. All persons including licensees, consultants, contractors and consumers who are related to the study, design,

construction and operation of thermal power generating facilities shall follow this Specific Requirements of

Electric Power Technical Standards for Thermal Power Generating Facilities.


Thermal Power Generating Facilities planned to construct and operate in the Kingdom of Cambodia shall be

as per the provision of this Technical Standards. In case a matter is not stipulated in the Technical Standards,

IEC Standards shall be applied. If it is not covered in the IEC standards, ISO Standards shall be applied. If it

is not covered in the ISO Standards, internationally recognized standards shall be applied, subject to the

approval by MIME.

Article 5: Facilities regulated in this Specific Requirements

A thermal power plant consists of three main components, a turbine/engine, a generator and a substation.

This Specific Requirements provides the requirements to regulate the generating facilities such as

turbine/engine and its accessories, and the generator including control systems, except the substation.

The requirements for the substation shall be in accordance with the Specific Requirements of Electric Power

Technical Standards for Transmission and Distribution.

Thermal power generating facilities regulated in this Specific Requirements of Electric Power Technical

Standards for Thermal Power Generating Facilities are following:

1- Steam Turbine Generating Facility

2- Gas Turbine Generating Facility

3- Internal Combustion Engine

4-Generator

86

CHAPTER 2

Requirements for all types of Thermal

Generating Facility

87

CHAPTER 2

Requirements for all types of Thermal Generating Facility

Article 6: Prevention of Electric Power Disasters from the Facility

The facilities shall be installed in such a manner that does not cause electrical shock, fire and other accidents.

The power facilities shall be installed with proper measures to protect operators from touching their moving

parts, hot parts and other dangerous parts, and to prevent them from falling accidentally.


Appropriate measures shall be taken to prevent third persons from entering compounds containing a power

plant. These measures shall include:

a. External fences or walls separated outside from inside compound. The height of external fences or

walls shall not be lower than 1,800 mm. Boundary clearance from the fences or the walls to the

electrical equipment shall not be less than the values described in the following table:

Table 1: Boundary Clearance from Walls or Fences to Electrical Equipment

Boundary clearance [mm] Nominal voltage

[kV]

A : Height of a wall or a fence

[mm] B : Wall C : Fence

(22) not less than 1,800 not less than 2,100 not less than 2,600



b. Signs to alert third persons to danger to be installed at the entrances/exits. Moreover, where

necessary, signs shall also be displayed on walls and fences.

c. Locking devices or other appropriate devices to be installed at the entrances / exits.

Article 8: Requirements related to the Fuel

1. Requirements related to Fuel Handling

a. Fuel handling shall be in accordance with the related laws.

b. Maintenance and safety checks of fuel facilities shall be implemented every day.

c. A responsible person for fuel facilities shall be designated.

d. The responsible person shall receive education and training regarding fuel handling every year.

88

2. Requirements related to Fuel Storage

a. Fuel storage tanks and fuel storage yards shall be in accordance with the related laws.

b. An appropriate vessel shall be used for the storage tank.

c. The storage yard shall be kept clean and appropriate signs shall be indicated in front of the storage

tank.

d. Necessary fire extinguishers or fire fighting systems shall be installed around the fuel storage area.

3. Requirements related to Fuel Transportation

a. Specifications of fuel transportation facilities or vehicles shall be in accordance with the related laws.

b. Working areas for fuel unloading shall be kept clean and appropriate lighting systems shall be

installed around the working area.

c. Working procedures for fuel transportation shall be prepared and be followed by the persons

concerned.

Article 9: Requirements related to the Handling of Chemical Materials

Handling of chemical materials at power plants shall follow the provisions of environment law and

regulations of the Kingdom of Cambodia.

Taking the characteristics of chemical materials to be used into consideration, appropriate measures against

those chemical materials shall be implemented and tools to protect against potential danger shall be installed.

Article 10: Requirements related to the Natural Disasters

Proper measures shall be taken to prevent failures of electric power facilities from anticipated natural disasters

such as floods, lightning, earthquakes and strong winds

Article 11: Requirements related to the Operation of Generating Facilities with Power System

When any generating facility has a serious fault, this facility shall be disconnected from the power system so

that the effect of the fault on the system can be minimized and the system could be operated continuously.

When a power system fault occurs in a system connected to a generating facility, the generating facility shall

be immediately disconnected from the system, so that the generator runs continuously with no-load while

waiting for the recovery of the system from fault. The next action shall be in accordance with procedures of

Grid Code and/or Distribution Code of the system.

Article 12 : Requirements related to the Environment

1. Compliance with Environmental Standards To prevent environmental pollution, the electric power facilities shall be constructed in accordance with

the environmental laws and regulations of the Kingdom of Cambodia.

89

2. Prohibition of Installation of Electrical Machines or Equipment Containing Polychlorinated

Biphenyls (PCBs)

a. The installation of new electrical equipment using insulating oil that contains greater than 0.005

percent (50ppm) polychlorinated biphenyls (PCBs) shall be prohibited.

b. The use of existing electrical equipment using material containing PCBs, if it was installed before the

Specific Requirements of Electric Power Technical Standards came into force, and effective and

sufficient measures shall be taken in order to prevent the material containing PCBs from escaping

from the oil container, shall be permitted.

c. Once removed from the electrical equipment, the material containing PCBs greater than 0.005

percent (50ppm) PCBs shall not be reinstalled in another electrical facility and shall be safely

scrapped as noxious industrial wastes.

Article 13: The Life of Electric Power Facilities

Electric power facilities shall be durable for long term usage with efficient and stable operation.

Article 14: Requirements related to the Design of Electric Power Facilities

With regard to the design of electric power facilities, selection of the materials, assembling and installation of

the equipment, suitable safety factors against foreseeable stresses, such as thermal stress, mechanical stress

and insulation strength shall be considered.

1. Insulation Co-ordination

Taking everything into consideration technically, economically and operationally, the insulation strength

of electrical equipment in the power plant shall be coordinated with the insulation of electrical

equipment in substations, transmission lines and distribution lines so that it may be in the most rational

conditions.

2. Dielectric Strength of Electrical Circuits

The dielectric strength of electrical circuits in the power plant shall be examined by dielectric strength

test, insulation resistance measurement and so on, to ensure that their performance corresponds to their

nominal voltage.

Moreover, before starting operation, the dielectric strength shall be confirmed by charging nominal-

voltage to the circuit continuously for 10 minutes.

However, if the nominal voltage of the electrical circuit is low-voltage, it can be tested by insulation

resistance measurement or leakage current measurement. In case of the leakage measurement, it is

sufficient to keep 1mA or less.

90

3. Mechanical Strength of Electrical Equipment against Short-circuit Current

All electrical equipment to be installed in the power plant shall be able to withstand the mechanical

shock caused by short-circuit current.

4. Thermal Strength of Electrical Equipment

Electrical equipment to be installed in the power plant shall be able to withstand the heat generated by

electrical equipment in normal operations.

5. Prevention of Damage of Pressure Tanks

Gas insulated equipment placed in the power plant shall be designed as following in order to avoid any

risk of damage:

a. Materials and structure of the parts receiving pressure shall be able to withstand the

maximum operating pressure and shall also be safe.

b. Parts receiving pressure shall be corrosion-resistant.

c. Insulation gas shall not be inflammable, corrosive or hazardous.

d. Tanks shall withstand the gas pressure rising during fault continuous time at internal failure

of gas insulated equipment.

Article 15: Requirements related to the Technical Document of Electric Power Facilities

To secure long term operation, each facility shall have its drawings, installation records, technical manuals,

instruction manuals and operation records necessary for its proper maintenance works. These documents

shall be safekept well.

Article 16: Requirements related to the Grounding

Grounding or other appropriate measures shall be provided for electrical equipment of thermal generating

facilities to prevent electrical shock, danger to human beings, fire, and other trouble to objects.

Grounding for electrical equipment shall be installed to ensure that current can safely and securely flow to the

ground. This grounding shall be in accordance with the types, the method and the resistance value of

grounding of each equipment provided in the Specific Requirements of Technical Standard for Transmission

and Distribution.

91

CHAPTER 3

Requirements for Steam Turbine Generating

Facility

92

CHAPTER 3

Requirements for Steam Turbine Generating Facility

Article 17: Steam Turbine Generating Facility

A steam turbine generating facility is a facility which generates electric power from the rotation of steam

turbine which rotates by the power of pressurized steam spoutted out from the boiler. Two main

components of the steam turbine generating facilty are the boiler and the steam turbine.

A boiler is a closed vessel in which water is heated under pressure. Then the steam from the boiler is used for

turbine rotation and preheating feed water.

A steam turbine is a mechanical device that can extract thermal energy from pressurized steam, which is

supplied from a boiler, and converts it into useful mechanical work to rotate the turbine. The steam turbine

consists of a rotor supported on bearings and enclosed in a cylindrical casing. The rotor is turned by steam,

which expands through nozzles and spouts out at a high speed against the moving blades to turn the

impellers.

93

PART 1

Boiler

Article 18: Requirements for Materials of Boiler and its Accessories

Vessels and tubes of the boiler, independent superheater and steam storage vessel and its accessories, and the

parts which are subject to an internal pressure higher than 0MPa (hereinafter, referred to as pressure parts)

shall be made of materials having sufficient mechanical strength and chemical stability under the maximum

working pressure and temperature.

“Sufficient mechanical strength” shall mean having good weldability, tensile strength, ductility, toughness,

hardness and other mechanical properties.

“Sufficient chemical stability” shall mean having character like good corrosion resistance, good heating

resistance and other chemical properties.

Article 19: Requirements for Structure of Boiler and its Accessories

1. Safety margins against the maximum stress

Structure of pressure parts of the vessels and tubes of the boiler shall have adequate safety margins

against the maximum stress under maximum working pressure or temperature condition. In this case, to

prevent the danger the stress shall keep the level not exceeding the allowable stress of the material. The

allowable tensile stress for each material shall be determined in accordance with its material temperature

condition.

To ensure adequate safety margins against the maximum stress, the structure of pressure parts of the

boiler and its accessories shall be able to withstand a water pressure test with a water pressure 1.5 times

as high as their respective maximum allowable working pressures without the occurrence of leakage.

The design pressure of economizers shall be not less than the maximum working pressure of the

economizer determined based on the maximum working pressure of the feed pump.

2. Prevention against Overheat

To prevent overheat of the water tubes in the furnace the following conditions shall be provided:

a. Boiler water shall be sufficiently circulated to the water tubes.

b. Boiler water shall be sufficiently purified. For this, proper measures such as a water softener, a

demineralizer, etc. shall be provided.

94

3. Protections against Flame

In case part of the boiler drum and tube heater are so constructed that they are exposed to flames or

high temperature gas, proper thermal protection, such as installation of a heat resisting tube material

and/or installation of a heat protection, or other suitable means shall be provided.

4. Considerations for Structural Strength

Where the effects of additional stresses such as spot concentration stress, repeated loads and thermal

stress are significant, suitable measurements such as increasing thickness shall be taken if necessary.

Article 20: Safety Valve for Vessels and Tubes of the Boiler

Vessels and tubes of the boiler which may be subjected to overpressure shall be equipped with safety valves

in order to release the pressure. In case of overpressure such as when the steam pressure of the boiler goes up

beyond regulation limits, safety valves shall be operated to release the pressure in order to prevent danger.

The safety valves for the boiler and its accessories shall have the following conditions:

a. The safety valves shall be installed in position that can be easily inspected.

b. At least, one safety valve shall be installed on the drum and one on the super-heater outlet.

c. The total capacity of the safety valves shall be not smaller than the maximum designed steam

capacity of the boiler.

d. At least one set pressure of the safety valves shall be not higher than the maximum allowable

pressure of any parts of the boiler (including superheaters and reheaters).

e. The safety valves shall be spring loaded safety valves or safety valves with a spring loaded pilot

valve.

Article 21: Feed Water System of Boiler

A feed water system is the system of equipment for feeding water to a boiler. The requirements for the feed

water system for boiler are the following:

- The feed water system shall be able to prevent thermal damage to the boiler during the

maximum evaporating condition.

- In order to prevent the thermal damage to the boiler caused by the feed water system's trouble,

the feed water system of the boiler shall be equipped with two or more means of water supply

equipment.

- The feed water system shall be able to independently supply a quantity of water not less than the

maximum designed steaming capacity of the boiler at any time and independently.

95

Article 22: Water Feeding and Steam Outpouring of Boiler

Water feeding and steam outpouring of boiler shall be required as follows:

- The steam outlet of the boiler shall be able to shut off the steam;

- The feed water inlet of the boiler shall be able to automatically and firmly shut off;

- A circulation boiler shall be equipped with a drain-off device which protects deposit and

regulates the water level.

Article 23: Monitoring the Running Condition of Boiler and Safety and Alarm System

The boiler and its accessories shall be equipped with the systems to monitor the running condition and the

alarm systems to prevent from the damage to the boiler and its accessories. The monitoring and alarm

systems as described above shall be equipped with devices as defining below:

1. For monitoring Circulation Boilers

a. Water level indicator in the boiler drum

b. Pressure indicator in the boiler drum

c. Temperature indicator at superheater and reheater outlet steam

2. For monitoring Once-through Boilers

a. Pressure indicator at superheater outlet steam

b. Temperature indicator at superheater and reheater outlet steam

3. For Safety and Alarm

The boiler shall be fitted with safety devices, which are capable of shutting off automatically the fuel

supply to all burners, and alarm devices which are capable to alarm when:

a. The flame vanishes

b. The water level falls (for circulation boiler drums)

c. The combustion air supply stops

4. For monitoring Boiler Water

The boilers shall be provided with means such as a water analyzer or other suitable devices to supervise

and control the quality of the feed water and boiler water.

* All above monitoring devices shall be installed in position that allows easy observation.

96

PART 2

Steam Turbine

Article 24: Requirements for Materials of Steam Turbine and its Accessories

Cylinders, vessels and tubes of the steam turbine and its accessories, and the pressure parts shall be made of

materials having sufficient mechanical strength such as good weldability, tensile strength, ductility, toughness,

hardness, and other mechanical properties and chemical stability such as having character like corrosion

resistance, abrasion resistance and other chemical properties under the maximum working pressure and

temperature.

Article 25: Mechanical Strength of Structure of Steam Turbine and its Accessories

Structure of steam turbines shall have sufficient mechanical strength such as having good weldability, tensile

strength, ductility, toughness, hardness and other mechanical properties, even when they are operated at the

speed, that the steam turbine reaches when the emergency governor is actuated. “Speed that the steam

turbine reaches when the emergency governor is actuated” shall include not only the actuated point of the

emergency governor but also the accelerated speed from the actuated point.

Structure of steam turbines shall have sufficient mechanical strength against the maximum amplitude value of

vibration produced on the major bearings and shafts. “Maximum amplitude value of vibration” shall mean

the maximum vibration reached during turbine operation including turbine start and stop operation.

The pressure parts and its accessories of the steam turbine shall have a sufficient safety margin against the

maximum stress under the maximum working pressure and shall not exceed the allowable stress of the

material.

A steam turbine and its accessories which are likely to be subjected to overpressure shall be equipped with an

overpressure protection device in order to release the pressure.

Article 26: Bearings of Steam Turbine

Bearings of steam turbines shall be constructed to be able to stably support the load during operation and

without the occurrence of abnormal wear and deformation and overheat. To prevent the bearings from “its

abnormal wear and deformation and overheat” the following measures shall be provided:

a. Steam turbines shall be equipped with main lubricating oil feed pumps, auxiliary oil pumps and

an emergency oil pump.

b. Quantity of lubricating oil for steam turbines shall be sufficient in all times.

c. Auxiliary oil pumps shall start automatically when the main oil pump out-put pressure becomes

abnormally low

97

d. An emergency oil pump or manual operation auxiliary oil pumps, which are installed for safety

stop of the main turbine when the main and/or auxiliary oil pumps have broken down.

e. The lubricating oil tank shall have necessary lubricating oil for the turbine.

f. Devices to clean lubricating oil shall be equipped

g. Device to control temperature of lubricating oil shall be equipped.


1. Speed Governor

A steam turbine shall be equipped with a system capable to adjust automatically the steam entering the steam

turbine in accordance with the actual speed of the turbine in order to prevent its speed and output from

fluctuating continuously even in case of a change in load condition. This system is called speed governor. The

speed governor consists of a speed monitoring device used for monitoring the actual speed of steam turbine

and then providing the order to a steam adjusting valve to adjust the quantity of steam flow entering the

steam turbine for the purpose to maintain speed of the turbine at the constant level. This speed governor

shall regulate the turbine speed not to reach the tripping speed even if the rated turbine output is shut down

instantaneously.

2. Emergency Speed Governor

In addition to a speed governor, a main turbine shall be equipped with an independent emergency speed

governor in order to prevent the speed from being increased abnormally. The emergency speed governor

shall be activated to interrupt the flow of steam to the turbine when the speed of turbine reaches the tripping

speed. The tripping speed of the turbine shall be at 110% (±1%) of the rated speed.

3. Normal Speed, Over Speed and Critical Speed of Turbine

Normal Speed of a steam turbine is the operational speed of the turbine when it normally loaded and when

the governor is in normal operation. The turbine shall be capable to operate at normal speed without any

restrictions upon the time and output. This normal speed shall be in between 98 to 101% of the rated speed

of the turbine. The normal speed of the turbine shall not be the speed remarkably less or more than the rated

speed.

Over-speed is the speed over than the normal speed which could do harm to the turbine.

Critical speed of a turbine is the speed which creates the resonance on the turbine. To avoid the damage of

the turbine caused by this resonance, the critical speed of the turbine combined with the generator on the

same shaft shall not be in the speed between the minimum speed controlled by the governor and the

maximum available speed of emergency stop device. However, it will be exempted if it will be arranged to

have enough countermeasure against the vibration at critical speed during operation of the turbine.

“Speed between the minimum speed controlled by the governor and the maximum available speed of the

emergency governor” is the speed can be operated by the steam turbine.

98

4. Limits of Turbine Speed

A turbine shall be capable to maintain the speed within the following limits:

a. Momentary variations shall be not more than 10% of the maximum rated speed when the rated

output of the generator is suddenly thrown off;

b. At all loads in a range between no load and the rated load, the permanent speed variation shall

be within ±5% of the maximum rated speed.

5. Protection against Over-speed

a. All main and auxiliary turbines (in case of turbine-driven boiler feed pumps) shall be equipped

with over-speed protective devices to prevent the turbine speed from being exceeded by more

than 10% of the normal speed of turbine.

b. In addition to the over-speed protective device, the main steam turbine shall be equipped with

a device capable to control the speed of the unloaded turbine without activating the over-speed

protective device into action.

Article 28: Requirements to Alarm and to Stop the Turbine in Emergency Case

In order to avoid the occurrence of damage from abnormal conditions (emergency case) during steam turbine

operation, the steam turbine shall be equipped with two systems: 1-protection system and 2-alarm system.

1. Emergency Protection System or Tripping System

In order to avoid the occurrence of damage from abnormal conditions, a main turbine shall be equipped with

a protection system which is capable to automatically shut off the steam supply to the turbine (automatic

emergency stop device) in the following cases:

a. Low lubricating oil pressure

b. High exhaust steam pressure

c. Low condenser vacuum

d. Over-speed

e. Emergency stop button is locally or remotely operated.

In addition to the automatic emergency stop device, the protection system shall have also a manual

emergency stop device.

When the above emergency stop device is actuated, the emergency stop alarm shall be energized.

2. Emergency Alarm System

The steam turbine shall be provided with alarm systems which give visual and audible alarm in the event of

abnormal conditions before steam shut off devices are activated. The abnormal conditions of steam turbine

operation can be indicated by the level of vibrations of the steam turbine.

99

When the maximum double amplitude value of vibrations of the major bearings or the shaft close to it is

detected to be beyond the allowable level during the turbine operation, the steam turbine operation is

considered as in abnormal condition.

The steam turbine shall be equipped with an alarm system, which gives an alarm when the maximum double

amplitude of vibrations of the major bearing or the shaft close to it exceeds the value shown in the table

below:

Table2: Allowable Level of Maximum Double Amplitude of Vibrations

Allowable level of the maximum double amplitude of vibrationsMeasurement

point

Rated speed

In case of speed less than

rated speed

In case of speed not less than

rated speed

3000 r/min 0.075 mm 0.062 mm Bearing pedestal

1500 r/min 0.105 mm 0.087 mm

3000 r/min 0.15 mm 0.125 mm Shaft 1500 r/min 0.21 mm 0.175 mm

3. Reviewing of Emergency Protection and Alarm System

For insuring the safety of steam turbine operation, before commercial operation of steam turbines, Licensee

shall submit to EAC for reviewing the following documents related to emergency protection and alarm

system:

a. Turbine protection system diagram

b. Explanation sheet for alarming and tripping set-points figure

Article 29: Monitoring the Condition of Turbine Operation

A steam turbine and its accessories shall be equipped with systems necessary to monitor the operating

condition and necessary alarm system to prevent any damages to the steam turbine and its accessories during

the operation.

Monitoring and alarm systems of steam turbines shall be capable to monitor the following data:

a. Rotational speed of the turbine

b. Main steam temperature and pressure (before main stop valve position)

c. Reheated steam temperature and pressure (before reheat stop valve position)

d. Steam turbine exhaust steam pressure

100

e. Lubricating oil inlet pressure of steam turbine bearings

f. Lubricating oil outlet temperature of steam turbine bearings or bearing metal temperature

g. Steam flow control valve position

h. Steam turbine vibration amplitude (with automatic recorder - media record is acceptable.)

Article 30: Reviewing the Safety of Steam Turbine and its Accessories

To ensure the safety of steam turbine operation, Licensees who plan to install a steam turbine in the

Kingdom of Cambodia shall submit the drawings and data related to the steam turbine on the items as

follows to EAC for reviewing the adoption of the requirements in this standard:

a. Turbine casings

b. Turbine rotors

c. Critical speed of turbine rotor

d. Technical data for strength calculations specified above

e. Material specifications of principal components

f. Assembly drawings

g. Control system diagram

h. Drawings and data which are deemed necessary by the Government

101

CHAPTER 4

Requirements for Gas Turbine Generating

Facility

102

CHAPTER 4

Requirements for Gas Turbine Generating Facility

Article 31: Gas Turbine Generating Facility

A gas turbine generating facility is a facility which generates electric power from the rotation of the gas

turbine which rotates by the power of the flow of combustion gas spoutted out from the combustor. In the

combustor, fuel is mixed with air and ignited, this combustion increases the temperature, velocity and volume

of the gas which expands through nozzles and spouts out at a high speed against the moving blades to turn

the impellers.

Main components of the gas turbine which are regulated by the requirements in this chapter are the

following:

- Turbine itself

- Bearings

- Governor

- Emergency stop and alarm device

- Overpressure protection device

- Monitoring and alarm system

Article 32: Requirements for Materials of Gas Turbine and its Accessories

Principal components of gas turbines which are subject to an internal pressure higher than 0MPa shall be

made of materials having enough mechanical strength such as having good weldability, tensile strength,

ductility, toughness, hardness and other mechanical properties and chemical stability such as good corrosion

resistance, good heating resistance and other chemical properties under the maximum working pressure and

temperature.

These principal components of gas turbines are following:

a. Rotors, stationary blades and moving blades of turbines

b. Rotors, stationary blades and moving blades of compressors

c. Turbines and compressor casings

d. Combustion chambers

e. Turbine output shafts

f. Connecting bolts for main components of turbines

g. Shaft coupling and bolts

h. Pipes, valves and fittings attached to turbines

The principal components of gas turbines excluding bolts, pipes, valves and fittings shall have been subjected

to the non-destructive tests.

103

The materials used in high temperature parts shall possess properties suitable for the design performance and

service life against corrosions, thermal stresses, creeps and relaxations.

In case where the base material coated with corrosion-resistant surfacing, the coating material shall be firmly

attached to the base material and shall not impair the strength of the base material.

The mechanical strength of all materials of gas turbines shall be confirmed to be sufficient through strength

calculation or other methods.

Article 33: Mechanical Strength of Structure of Gas Turbine and its Accessories

Structure of gas turbines shall have sufficient mechanical strength such as having good weldability, tensile

strength, ductility, toughness, hardness and other mechanical properties even when it is operated at the speed

that the gas turbine reaches when the emergency speed governor is actuated. Even if the rotational speed of

the gas turbine exceeds the rated rotational speed for any reasons and an emergency speed governor is

actuated, the turbine shall not be damaged.

Structure of gas turbines shall have sufficient mechanical strength against the maximum amplitude value of

vibration produced on the major bearings and shaft. “Maximum amplitude value of vibration” shall mean the

maximum vibration reached during turbine operation including turbine start and stop operation.

The pressure parts and their accessories of the steam turbine shall have a sufficient safety margin against the

maximum stress under maximum working pressure and temperature. In this case, the stress shall not exceed

the allowable stress of the material. To ensure the sufficient safety margin again the maximum stress, the

structure of pressure parts of the gas turbine and its accessories shall be able to withstand a water pressure

test with a water pressure 1.5 times as high as their respective maximum allowable working pressures without

leakage.

Gas turbine and its accessories which are likely to be subjected to overpressure shall be equipped with an

overpressure protection device in order to release the pressure.

Article 34: Bearings of Gas Turbine

Bearings of gas turbines shall be constructed to be able to stably support the load during operation and

without the occurrence of abnormal wear and deformation, and overheat. To prevent the “abnormal wear

and deformation and overheat” of bearings, the gas turbine shall be equipped with the following lubricating

oil feed pumps to provide the satisfactory lubricating oil to the bearings:

a. Main lubricating oil feed pumps

While the turbine is operating, the main lubricating oil feed pumps shall be operated to provide a

satisfactory lubricating oil to the bearing of the gas turbine.

104

b. Auxiliary oil pumps

Auxiliary oil pumps shall automatically start when the main oil pump out-put pressure becomes

abnormally low

However, if a gas turbine is equipped with a device to automatically shut off the inflow of fuel

and safety stop when the outlet pressure of a main oil pump decreases, it is not required to equip

an auxiliary oil pump.

c. Emergency oil pump

An emergency oil pump or manual operation auxiliary oil pumps shall be installed for safety stop

of the main turbine when main and/or auxiliary oil pumps have broken down.


1. Speed Governor

A gas turbine shall be equipped with a device capable to automatically adjust the flow of fuel entering the gas

turbine in order to prevent its speed and output from fluctuating continuously even in case of a change in

load condition. The device to automatically adjust the flow of fuel entering into the gas turbine automatically

is called Speed Governor. This Speed Governor shall have an ability to hold the turbine speed after the

interruption of the rated load below the speed at which the emergency governor is actuated.

Even the gas turbines without direct fuel burning shall be equipped with a device to control the maximum

rotational speed.

2. Normal Speed, Over-Speed and Critial Speed of Gas Turbine

Normal Speed of a gas turbine is the operational speed of the turbine when it normally loaded and when the

governor is in normal operation. The turbine shall be capable to operate at normal speed without any

restrictions upon the time and output. This Normal Speed shall be in between 98 to 101% of the rated speed

of the turbine. The normal speed of the turbine shall not be the speed remarkably less or more than the rated

speed.

Over-speed is the speed over than the normal speed which could do harm to the turbine.

Critical speed of a turbine is the speed which creates the resonance on the turbine. To avoid the damage of

the turbine caused by this resonance, the critical speed of the turbine combined with the generator on the

same shaft shall not be in the speed between the minimum speed of governor and the maximum available

speed of emergency stop device. However, it will be exempted if it will be arranged to have enough

countermeasure against the vibration at critical speed during operation of the turbine.

“Speed between the minimum speed of governor and the maximum available speed of emergency stop

device” is the speed can be operated by the steam turbine.

105

“The minimum speed of governor” shall mean the following;

a. The minimum speed in speed variation when the turbine is not combined with a generator or a

rotor.

b. The minimum speed of grid frequency when the turbine is combined with a generator or a rotor.

Article 36: Emergency Alarm and Stop Devices

In order to avoid the occurrence of damage from over-speed and abnormal conditions (emergency case)

during operation, the gas turbine shall be equipped with two devices: 1-Emergency Stop Device and 2-

Emergency Alarm Device.

1. Emergency Stop Device

In order to avoid the occurrence of damage from over-speed or other abnormal conditions during gas turbine

operation, the gas turbine shall be equipped with a device which automatically interrupts the inflow of fuel or

gas called Automatic Emergency Stop Device. In addition to the Automatic Emergency Stop Device, the gas

turbine shall be also equipped with a manual emergency stop device. When the above emergency stop device

is actuated, the emergency stop alarm shall be activated.

In case of over-speeds or speeds exceeded the rated speed of the gas turbine, the automatic emergency stop

device shall be actuated to stop the turbine when the speed reaches the tripping speed. The tripping speed of

the turbine shall be at 110% (±1%) of the rated speed.

“Other abnormal conditions” are the following cases:

a. The case where an internal failure occurs in a generator.

b. The case where the gas temperature significantly increases.

c. The case where the lubricating oil temperature significantly increases.

d. The case where the lubricating oil pressure significantly decreases.

2. Emergency Alarm Device

A gas turbine shall be equipped with a device that functions to provide an alarm when the amplitude value of

vibrations is detected to be beyond the allowable level during the gas turbine operation.


A gas turbine and its accessories shall be equipped with systems necessary to monitor the operating condition

and alarm system to prevent any damages of the gas turbine and its accessories during the operation.

106

Monitoring systems of gas turbines shall be capable to monitor the following data:

a. Rotational speed of the turbine (Gas turbine tachometer)

b. Outlet pressure of an air compressor of gas turbine

c. Gas temperature at the inlet of a gas turbine (The calculation method to determine the inlet

temperature of gas based on the measured outlet temperature of the gas is applicable.)

d. Lubricating oil inlet pressure of gas turbine bearings

e. Lubricating oil outlet temperature of gas turbine bearings or bearing metal temperature

Alarm systems of gas turbines shall provide an alarm when the following situations occur:

a. Temperature of inlet or outlet gas of gas turbine is high

b. Lubricating oil pressure is low (shall alarm before the function of the emergency stopping

device.)

c. Fuel oil supply pressure is low.

Article 38: Reviewing the Safety of Gas Turbine

To ensure the safety of gas turbine operation, Licensees who plans to install gas turbine in The Kingdom of

Cambodia shall submit the drawings and data related to the gas turbine on the items as follows to EAC for

reviewing the adoption of safety requirements in this standard:

a. Combustion chambers

b. Piping arrangements fitted to turbines (including fuel, lubricating oil and cooling water system)

c. Particulars (type of turbine, power and rotation speed of turbine, gas pressure and temperatures

at turbine inlet and outlet, ambient condition, service fuel and lubricating oil)

d. Material specifications of principal components

e. General arrangement

f. Control system diagram

g. Calculation sheets for vibration of turbine blades

Article 39: Requirements for Gas-Turbine Combined Cycle and its Accessories

Gas turbine combined cycle plants and their accessories shall be designed, manufactured, constructed and

operated in accordance with the requirements in this chapter and chapter 3.

107

CHAPTER 4

Requirements for Gas Turbine Generating

Facility

108

CHAPTER 5

Requirements for Internal Combustion Engine

Article 40: Internal Combustion Engine

A generating facility by an internal combustion engine is a facility where the generator is rotated by the

internal combustion engine to generate the electric power. The internal combustion engine is a engine in

which the fuel is mixed with air and burnt in confined space called a combustion chamber. The combustion

of mixed fuel and air in the combustion chamber creates gases of high temperature and pressure which

moves the moving parts of the engine such as pistons, rotors.

Main components of the internal combustion engine which are regulated by the requirements in this chapter

are the following:

- Engine itself

- Bearings

- Governor

- Emergency stop and alarm device

- Overpressure protection device

- Monitoring and alarm system

Article 41: Requirements for Materials of Internal Combustion Engine

Cylinders, vessels and tubes of the internal combustion engine and its accessories and the pressure parts shall

be made of the materials which have sufficient mechanical strength such as having good weldability, tensile

strength, ductility, toughness, hardness and other mechanical properties and chemical stability such as good

corrosion resistance, good heating resistance, and other chemical properties under the maximum working

pressure and temperature.

The scope of properties of materials shall be chosen according to the specific conditions of use.

Article 42: Mechanical Strength of Structure of Internal Combustion Engine

Structure of an internal combustion engine shall have sufficient mechanical strength such as having good

weldability, tensile strength, ductility, toughness, hardness and other mechanical properties even when it is

operated at the speed that the engine reaches when the emergency speed governor is actuated. Even if the

rotational speed of the engine exceeds the rated rotational speed for any reasons and the emergency speed

governor is activated, the machine shall not be damaged.

109

Pressure parts and their accessories of the internal combustion shall have a sufficient safety margin against

the maximum stress under the maximum working pressure and temperature. In this case, the stress shall not

exceed the allowable stress of the material.

To provide “sufficient safety margins” to the pressure parts and their accessories, the following conditions

shall be fulfilled:

a. Combustion chamber and pipes of the ancillary equipment for internal combustion engines shall

meet the requirement of good weldability, tensile strength, ductility, toughness, hardness and

other properties.

b. Internal combustion engines and ancillary equipment shall meet the requirement of corrosion

resistance and abrasion resistance, if it’s necessary.

c. The pressure parts of internal combustion engines and their accessories shall be able to

withstand a water pressure test using a water pressure 1.5 times their respective maximum

allowable working pressures without leakage.

d. However, the water pressure test is not required for;

(i) Internal combustion engine’s casing which has the result of a water pressure test that was

conducted under the same structure and same material conditions.

(ii) Internal combustion engines, the strength of which has been proven theoretically by

calculation to have the mechanical strength to resist a water-pressure of 1.5 times of the

maximum allowable pressure.

Article 43: Bearings of Internal Combustion Engine

Bearings of the internal combustion engine shall be structurally able to stably support the load during

operation and without the occurrence of abnormal wear, deformation and overheat.

For the bearings with lubricating oil system to prevent the abnormal wear and deformation and overheat of

bearings the following conditions shall be provided:

a. The main lubricating oil pump shall be capable to feed sufficient lubricating oil to the engine during normal conditions

b. The lubricating oil tank shall be capable to store the quantity of lubricating oil required for the engine.

c. Devices capable to clean the lubricating oil (An oil filter which has the capacity to clean the lubricating oil can be one of them.) shall be equipped.

d. Devices capable to regulate the temperature of the lubricating oil (An oil cooler for controlling the oil temperature, which may be automatic or manual, can be one of them.) shall be equipped.

110

Bearings without lubricating oil system shall also be regarded as satisfactory if their technical mechanism is

proved to be sufficient for the required level of safety.

Article 44: Governance of Internal Combustion Engine Speed

An internal combustion engine shall be equipped with a device to automatically adjust the fuel entering the

engine in order to prevent its speed and output from fluctuating continuously even in case of a change in load

condition. This device is called a speed governor. Speed governors shall be capable of preventing the

rotational speed and output of the engine from hunting in case of any changes. The maximum rotational

speed shall be controlled in the range lower than the speed at which the emergency speed governor is

actuated, even when the rated load is cut off.

Article 45: Emergency Stop and Alarm Devices

In order to avoid the occurrence of damage from over-speed or other abnormal conditions during the engine

operation, the internal combustion engine shall be equipped with an automatic emergency stop device, a

manual emergency stop device and emergency alarm device. Emergency stop device automatically interrupts

the inflow of fuel. When the above emergency stop device is actuated, the emergency stop alarm shall be

activated. “Over-speed” in this article is the state which an internal combustion engine speed exceeds its rated

rotational speed. “Other abnormal conditions” in this article is the state with an excessive rise of the cooling

water temperature, the accidental stoppage of the cooling water feed and so on.

All internal combustion engines except those with a rated output less than 3000kW shall be equipped with an

emergency governor which is actuated to stop the engine at a speed higher than engine rated speed but not

higher than 1.16 times of this rated speed.

All internal combustion engines except those with a rated output less than 3000kW shall be equipped with a

device which stops the fuel flow automatically in case the cooling water temperature rises abnormally or the

cooling water feeding stops.

Article 46: Overpressure Protection Devices

An engine and its accessories which are likely to be subjected to overpressure shall be equipped with an

overpressure protection device in order to release the pressure such as relief valve which shall have a

sufficient capacity for preventing overpressure, and shall activate at a pressure lower than the maximum

pressure.

“An engine and its accessories are likely to be subjected to overpressure” means the following parts:

a. Cylinders with a diameter of more than 230mm and the maximum allowable pressure of more

than 3.4 MPa (excluding gas fuel engines).

b. Sealed crankcases in the cylinders with a diameter of more than 250mm.

111


An engine shall be equipped with systems necessary to monitor the operating condition and systems

necessary to provide an alarm to prevent damages to the engine and its accessories during the operation.

Monitoring systems of internal combustion engines shall be capable to monitor the following data:

a. The rotation speed of the internal combustion engine

b. The temperature of the cooling water at the outlet of the internal combustion engine

c. The pressure of the lubricating oil at the inlet of the internal combustion engine

d. The temperature of the lubricating oil at the outlet of the internal combustion engine

112

CHAPTER 6


113

CHAPTER 6


Article 48: Protection of Generators

Thermal power generators shall be equipped with a protection device against any over-current accident.

The thermal power generators shall be also equipped with devices to automatically cut off the generator from

the electrical line when:

a. Over-current occurs.

b. Internal failures, such as grounding or short-circuit of stator windings, of the generator with a

capacity of 3000kVA or more occurs.

c. The thrust bearings of the turbine with a rated capacity of 3000kW or more are significantly

worn down and there is a significant rise in the temperature of the bearings.

Article 49: Electrical Equipment

Electrical equipment installed in thermal power plants shall be designed and constructed so that it structurally

allows easy operation, inspection, overhauls and repairs.

Article 50: Cables in Thermal Power Plants

Cables used in thermal power plants shall be installed so that the original properties of non-flammability are

not impaired.

In case cables are installed in such hazardous areas that there is a risk of fire or explosion in the event of an

electrical fault, proper protections against such risks shall be provided.

Cables and wires shall be installed and supported so that they will not be damaged by any mechanical stress.

Article 51: Installation of Hydrogen Cooling Type Generators

The hydrogen cooling system is usually adopted in a large capacity generator. Such generators are filled with

hydrogen to cool all windings of generator. Because hydrogen explodes if it is mixed with air, the following

measures against the explosion shall be taken for the generator with the hydrogen cooling system:

1. The generator shall be structurally constructed so that the hydrogen will not leak to the outside

and the air will not go into the inside.

114

2. The structure of the generator shall have sufficient mechanical strength (explosion-proof

construction) to withstand pressure generated by hydrogen explosion.

3. The generator shall be equipped with an alarm device to be activated when purity of hydrogen

decreases to 85% or less. Moreover, the device shall raise an alarm when pressure and/or

temperature of the hydrogen change remarkably.

4. Tubes and valves filled with hydrogen shall have the structure to prevent hydrogen leakage. The

tubes shall be a copper pipe or a seamless steel pipe.

5. When the hydrogen leaks from the shaft seal part of the generator, the gas leakage shall be

stopped and the gas shall be safely discharged outside.

Article 52: Control Systems

The control system for generators shall have the integrated interlocking system to properly and safely control

the generator.

Annunciators shall be provided for detection of abnormal operating conditions and shall be equipped with

emergency trip functions necessary to assure equipment integrity and overall plant safety. The annunciator

and trip functions shall be implemented through each independent device.

The control system shall have a function to start up and shut down the generator. The thermal power plant

including the generator shall be started up and shut down manually from the control panel and automatically

through the individual sequence programs.

115

CHAPTER 7


116

CHAPTER 7


Article 53: Transitional Provisions for Small and Medium Licensees

Requirements in this chapter are the minimum requirements and temporarily applicable to generation

facilities of small and medium licensees when their generation facilities are in the transitional stage taking into

consideration present level of existing generation facilities in Cambodia. Therefore these requirements will be

cancelled in the future by Ministry of Industry, Mines and Energy when the generation facilities of Licensees

in Cambodia passed the transitional stage.

“Small licensee” means the licensees with an installed capacity of less than 500 kW.

“Medium licensee” means the licensees with an installed capacity from 500kW up to 3000kW.

The minimum requirements to temporary apply to generation facilities of small and medium licensees are

described in the following articles in this chapter.


For prevention of electric power disasters, all power generating facilities of small and medium licensees which

are in the transitional stage at present shall be at least in accordance with the following minimum

requirements:

- A generator circuit breaker shall be equipped to each generator.

- A bare conductor is allowed only when it is installed inside of the panel or box.

- A naked knife-switch is allowed only when it is installed inside of the panel or box.

- Each cable shall have the cable number attached.

- Electrical facilities shall be grounded appropriately.

- All power cables and control cables shall be installed inside the cable tray or conduit pipe in the

facility area.


For prevention of danger to third persons, all power generating facilities of small and medium licensees which

are in the transitional stage at present shall be at least in accordance with the following minimum

requirements:

117

- Fences and/or walls shall be installed around the generating facilities to prevent third persons’

accidents.

- The entrances/exits of above fences or walls needs appropriate key lock systems.

- “Keep out” signs shall be indicated at the entrance of generating facilities.

- Generating facility area shall be kept clean.

- All rotating and working parts shall be covered and protected from workers’ accidents.

- Any belt drive power transmission systems shall be not approvable.

Article 56: Safety Measures for Fuel and Chemical Materials

For safety in using fuel and chemical materials, all power generating facilities of small and medium licensees

which are in the transitional stage at present shall be provided with the following measures:

- Fire fighting systems and/or extinguishers shall be equipped near the fuel storage area.

- Fuel tanks shall be equipped at least 1 (one) meter away from electrical facilities.

- Fuel tanks shall be equipped solidly and combustible materials shall not be left within 1 (one)

meter.

- Exhaust gas shall be discharged at least 2(two) meters high outside of the building.

- Exhaust pipes and/or hot parts of engines shall be protected.


- Noise of generating facilities shall be prevented in residential areas. (Refer to related laws).

Table 3: Countermeasures for Preventing Noise of Generating Facilities

Operation case Countermeasures

Interval operations (except night time) ------

24 hours operation (including night time) Generation facilities shall be enclosed by walls or

installed in a specific building.

- Waste oil shall not be discharged directly to the ground in order to prevent soil pollution and

protecting well water.

Article 58: Requirements for Operation

1. Monitoring Devices

Generators and generating facilities shall be equipped with the following monitoring devices:

a. Generator volt meter

118

b. Generator ammeter

c. Generator frequency meter

d. Energy meter (kWh)

e. Generator out put (kW) meter

g. Fuel tank level (or fuel flow meter)

h. Engine oil pressure meter

i. Engine oil temperature meter (if any)

j. Cooling water temperature (if any)

2. Record Requirements and Maintenance of Generating Facilities

- Daily operational data, such as generated energy (kWh), Voltage, frequency, operation time and

all instrument data, shall be recorded.

- Considering the operational period, overhaul of the engines shall be scheduled and implemented.

- Maintenance records including replacement parts and checking points shall be established.

3. Report Requirement

The following reports shall be submitted to EAC and copied to MIME every year:

a. Operation records

b. Maintenance records

c. Trouble records

If any trouble or accidents in relation to the generating facilities occurs, the licensee shall report to EAC

without delay.

Article 59: Safety and Technical Training

“Small and Medium Licensee” and/or technical staff who operate and maintain their facilities shall pass a

training school program or course recognized by MIME or EAC. The technical training shall be provided to

refresh their memory within three years or less.